Flash doesn't just have a set list, he uses his general intelligence exhaustively during games - and he still loses a lot from being too predictable, too routine, producing the same responses to the same stimuli - even though his macro mechanics and builds are utterly top-notch.
Players triple and quadruple guess each other as they decide what build to use, where to place a proxy, how to scout, whether to scout, how to fake a proxy or allin, how to pretend like you're faking a proxy or allin but actually do the allin or a different proxy or allin or just do two half baked allins in a row to fake out your opponent into your real timing attack which might actually be a double fast expand while they're confused.
When you scan a player and see a tech lab on a starport, are they building banshees? Are they faking you out? Even if you've run stats on them, maybe they have a history of never building banshees, and they're using it in a key game because they know you won't expect it.
So any single action in the game has to be placed into a context. Depending on that context, a tiny factor which is irrelevant in one game can be key in another.
For me, the mechanical things are a zen thing. It's almost like a sort of meditation; your mind falls into these practiced routines, but you have to juggle all of them at the same time, choose which ones you can afford to let fall (since you can't do everything at once,) and then have your higher order tactical and strategical decisions on top of it. I haven't ever done anything else which engages my mind in the same way, and it certainly wouldn't do so without the mechanical demand you can never truly fulfill.
