I think I've figured out the source of 90% of my wrong keypresses.

[ViolaCrossfire]

You must be joking. Why do you like a GCD where you can go to the toilet ... AND wash your hands and still be in time to press your second button.

Because random procs exist along with boss mechanics. OGCD's also fill up the slack of GCD downtime. Not to mention traveltime needed for positionals.