Don't underestimate the value of spell hit.

446 is a magic number.

This is because, as casters — untalented, alone, completely naked and bereft of any helpful companions or raid buffs — our spells have a 17% chance to miss an enemy three levels above us."... But I'm level 80!" you exclaim, brandishing your fiery-enchanted Titansteel Spell Blade.  "What could possibly be three levels above me, Elder Idotyou the Love Fool of Stormwind, Ironforge and Darnassus, Champion of the Frozen Wastes and SomethingelseIcan'tremember?"

Oh, nothing much.  Just every skull-level raid boss in the entire endgame, from the creepy, crawly Anub'rekahn to also creepy but considerably less crawly Yogg-Saron.

In order to minimize — and, ultimately, eliminate — this inherent chance to miss, we stack spell hit, via talents, gear, gems, enchants, food buffs and slavery.  (Oh, you hadn't heard?  Warlocks can look forward to a new 3.2 ability called "Enslave Shadow Priest."  I fully intend to name mine Abigore.)

At the current hit cap of 446, our chance to miss is exactly zero.

Sources of Spell Hit

Although our primary source of spell hit comes from gear — such the appropriately named (as in, I will curse you with my dying breath you thrice-damned trinket!) Dying Curse, which waited until the week after I rerolled Shaman to drop three times in the same Heroic Naxxramas raid — ...

Wait, where was I going with this?

Oh, right.  Gear is a source of spell hit, but it is far the only source:

• The Affliction talent, Suppression, grants a maximum of +3% hit.
• A balance druid spec'd into Improved Faerie Fire will provide the entire raid with +3% hit.  Of course, this assumes that the druid not only (1) survives the encounter, but also (2) maintains 100% uptime.
• Alternately, a shadow priest spec'd into Misery will provide the same +3% hit with the same caveats.  Note that Misery does not stack with Improved Faerie Fire.
• The Draenei racial, Heroic Presence, provides an additional +1% hit to party members.  Heroic Presence does stack with either Improved Faerie Fire or Misery, but not both.

This means that a Horde warlock such as myself needs need to make up (a) 14% hit if spec'd 3/3 Suppression or raiding with a properly spec'd balance druid or shadow priest, or (b) 11% hit if spec'd 3/3 Suppression and raiding with a properly spec'd balance druid or shadow priest.

What if you're not a Horde warlock?  What if you're something confusing, like a Draenei shaman, a Night Elf druid or a human shadow priest in a xenophobic role-playing guild that is convinced that those loveable Spacegoats are actually Eredar (and wouldn't be caught dead sharing a raid ID with one)?

First, if you're not a Forsaken warlock, you totally should be.  Go down to Old Stratholme, eat a plagued muffin and call Sylvannas in the morning.

Second, and as an interim solution, try WoWWiki.  Or ask Amber — very, very nicely — to make a flowchart.

We made a flowchart.  Once.

Our felpuppy eated it.

The Mechanics of Spell Hit

In a recent blogpost, Hydra of Almost Evil advised her readers to avoid gemming for spell hit at the expense of spell power — even if they happened to be under hit cap at the time. With all due respect to our vertically challenged sistren, this is fantastically awful advice.  Don't follow it ... or, at least, don't follow it blindly.

To understand why, it's important to understand the mechanics underlying spell hit.

Remember those incredibly dorky table top roleplaying games that all the ner—  ... I mean, all the perfectly nice, normal, well-adjusted kids (such as my boyfriend, who I love dearly <3) played in high school?  Those games used dice to determine pretty much everything.

Does my unnaturally handsome, inhumanly powerful, Orlando Bloom-lookalike of a half-elven, half-vampire rogue manage to stab the fire-breathing dragon in the heart with a butter knife?

Roll 2d20 to find out!

WoW works the same way.  The game rolls once to determine if a spell hits.  Then, assuming it does, it rolls again to determine if the spell crits.  If you're spell hit capped, then your spells will always hit.  If not, they will miss at a rate approximately equal to the difference between the spell hit cap and your actual hit rating.  If you have +12% hit (an amount Hydra feels is sufficient), then you will miss approximately 5% of the time (17% - 12% = 5%) against a level 83 mob.

At a glance, this doesn't sound too terribly bad.  If you cast 100 Shadow Bolts over the course of a fight, only five of them will miss.  So, if you stack spellpower over spell hit, maybe the extra oomph you've packed into the 95 Shadow Bolts that do hit will make up for the 5 that don't.  Maybe the math will even work out so that 95 Super Shadow Bolts deal more damage than 100 boring old Clark Kent flavored ones.

This is Hydra's logic — and, to be fair, I've seen it repeated elsewhere on the internether, including my own /guild chat.

The thing is, it's a rather shallow view that doesn't take into account the synergies that exist between our various stats and spells.

Spell Hit vs. Spellpower and Spell Crit

First, if a spell doesn't hit, then your spellpower and spell crit are worth exactly nothing.  I'm sure you've heard this before: if a spell doesn't hit, it can't crit.  This means that if you have +32% crit chance but are 5% under hit cap, then you actually have +30.40% crit chance.  If you have 2K spellpower but are 5% under hit cap, then you actually have 1.9K spellpower.

The Cost of a Miss

Second, and contrary to widely held belief, the cost of a missed spell is not equal to the opportunity cost of the lost cast time.  It's actually much higher.

For a relatively straightforward example, hearken back to the bygone days of The Burning Crusade, when all raiding warlocks specced shadow-mage and had a wonderfully complex rotation that looked something like this:

Shadow Bolt
Shadow Bolt
Shadow Bolt

If your Shadow Bolts were hitting for 5K and critting for 10K approximately 30% of the time, then it would have been tempting to claim that the "cost" of a miss was 5K + .3(10K) = 8K.  Assuming a 3 second cast time with 5% chance to miss, you would lose approximately 48K damage (or six Shadow Bolts) over the course of a five minute fight.  If by foregoing spell hit you could stack enough spellpower to sufficiently boost each Shadow Bolt's damage to make up for that ... it would be a wash, right?

Not entirely.  The old Improved Shadow Bolt talent caused our Shadow Bolt crits to place a stacking debuff on the target that increased the next four shadow-based attacks (and all shadow-based DoT damage in between!) by 20%.  Therefore, the cost of a miss wasn't just the lost DPS from the shadowbolt that fizzled and died in mid-air; it was also the lost DPS from reduced uptime on Improved Shadow Bolt.

And that was a straightforward example — one that doesn't even exist in our current world!  Our rotations are much more complicated now, so the cost of a miss is significantly higher.

The actual math is beyond the scope of this blog (I crunch numbers for a living, so I can't quite bring myself to do it in my downtime), but the theory behind it is fairly obvious.

Haunt is the mainstay of an Affliction rotation.  It has a cast time, a travel time, deals a small amount of damage, procs Shadow Embrace and increases all shadow-based periodic damage done to the target over the course of its 12 second duration.  It also refreshes Corruption via Everlasting Affliction and returns health to the warlock whenever it expires or is refreshed.

So.  What happens if Haunt misses?

It goes on cooldown and can't be cast again for 8 seconds.  Even if you've attempted to precast it, the 12 second duration and 8 second cooldown mean that the Haunt debuff will fall off your target.  Depending upon timing, it's entirely possible that Corruption or Shadow Embrace could expire as well.  If so, Corruption will need to recast at the cost of a Global Cooldown.  Your next Shadow Bolt will re-apply Shadow Embrace, but — again, depending upon timing — you may not be able to cast a Shadow Bolt immediately because your priority is refreshing Unstable Affliction (which fell off while you were reapplying Corruption) and then Curse of Agony (which fell off while you were casting Unstable Affliction).

In other words: one missed spell could wreak havoc on your entire rotation, not to mention cost you substantially more in lost DPS than you could have gained from the spell alone.

This isn't unique to Affliction rotations, either.  A Destruction warlock who misses a Conflagrate in the last five seconds of Immolate's duration forgoes not only Conflagrate's base damage but also the 25% boost from Immolate.  Incinerate or Shadow Bolt misses lead to fewer Nightfall or Backlash procs, and — for Demonology warlocks or Demo/Destro hybrids — an Incinerate miss during a Decimation phase translates into lost DPS not only from Incinerate but from Soulfire as well.

The TL;DR is that the cost of a miss is seldom just the DPS from the spell that missed.  This is because for all three talent trees, misses tend to set off a chain reaction of events that could have been avoided had we simply stacked spell hit to cap and then worried about rounding out our other stats.

Diminishing Returns

That said, spell hit does suffer from diminishing returns.  As you approach the spell hit cap and your percent chance to miss decreases, the value of each additional point of hit becomes progressively smaller.  In other words, the less hit you have, the more important it is to stack — whereas the more hit you have, the less each individual point of hit is worth relative to stats like spellpower or critical strike.

This is why it's so hard to rank gear, and why I personally have never bothered with a "BiS loot list" or a definitive gear plan.  Even for a warlock below cap, an item with spell hit isn't necessarily an upgrade over an item without it; each individual piece has to be viewed within the context of your entire gear set, and assessed for what it adds versus what it takes away.

Gemming and Talenting for Hit

So, what does this mean for a raiding warlock, struggling to balance spell hit with spellpower, spirit, spell haste and critical strike?

In general, I recommend gemming and talenting for hit until you are spell hit capped from gear alone.  I love socket bonuses — in part because I'm OCD, and in part because free stats are free stats! — so I tend to use Rigid Autumn's Glow (+16 hit) in yellow sockets, Veiled Monarch Topaz (+8 hit, +9 spellpower) in red sockets and Purified Twilight Opal (+9 spellpower, +9 spirit) in blue sockets ... provided, of course, that the socket bonuses are worth picking up in the first place.

It's also worth noting that one Runed Scarlet Ruby and one Rigid Autumn's Glow provide the same amount of hit and one more point of spellpower than two Veiled Monarch Topazes — so if you ever find yourself in a position of needing exactly 16 more hit, I'd suggest socketing those in a red and yellow socket, respectively, over stacking two Veiled Monarch Topazes.

Once you are spell hit capped from gear, you can start swapping out hit gems for spellpower gems.

A Hit Set vs. an Output Set?

You don't need a hit set, per se.  If for some reason you find yourself with two versions of the same chest (like I did, thanks to an overabundance of Conqueror tokens and far too many Undying attempts), and you find yourself tempted to gem one for raw spellpower and the other for spell hit for more situational use ... hey, that works!

Personally, I'd recommend looking for one or two hit-heavy pieces (preferably totaling about +3% hit) that you can use in raids when you don't have a shadow priest or balance druid around to provide hit via Misery or Imp'd FF.  I still use the Ward of the Violet Citadel (combined with the Leggings of Atrophy) for this purpose.  As an offhand, the Ward is especially nice because can be equipped in combat if the critchicken or shadow priest happens to eat a landmine in Mimiron, Phase 1.5.

... not that that's ever happened to our raid, of course. >.>

In Conclusion ...

• Misses are bad, and the true cost of a miss is often much higher than the DPS of the missed spell.
• Spell hit has diminishing returns; the closer you are to spell hit cap, the less valuable each additional point of spell hit is relative to other stats (like spellpower and critical strike).
• Gem and talent for spell hit until you achieve cap from gear alone.  Then revisit your talent trees or start switching out hit gems for output gems.
• It may be worth spending DKP on a couple of pieces with spell hit that can be used situationally.
• Critchickens and shadow priests are wonderful things.  Love them.  Cherish them.  (Or use them and abuse them —  but don't let them catch on!)