Johannes
Arcane
Matching your upgrade timing to your attack is just logical, there's still room to alter the timing you sync them at.It's not a single correct way, but a handful of them, and you scout to find out which one the opponent did. Though there have certainly been times when a particular opening for a given matchup was so dominant it wasn't even really necessary, aside from avoiding cheese.If there was just a single correct way to open, why would people bother scouting?
Again, you can't alter these timings because it makes the entire build irrelevant. You need your relevant upgrade to happen before you reach the enemy base, and doing it any earlier than that means you didn't build as many units as you could have. In either case you effectively just lose right there. You can't upgrade your marines with stim after they're all dead. You may as well try adding ingredients to a lasagna after it's in the oven.
These people literally figure out what build the opponent is doing by looking at their gas production and checking the amount of gas left vs the clock. The only way that conceivably works is when the builds are incredibly predictable.
Scouting isn't a one off thing, but something you constantly want to do to know what the opponent is doing minute to minute, builds aren't set in stone as you commit into this or that. You have a lot of opportunity to catch your opponent off guard in the early game, in SC2 too.