I am going to have this needlepointed on a cushion one day:
"Do not ever, ever, ever try to be the boss of gauge."
Because gauge will be the boss of you. Gauge is not static. It can change with the day. There's a reason that outside of the U.S., a swatch is called a "tension square". How tense or relaxed you are at any given time is going to affect how your knitting turns out. If you are, say, trying to complete a hat in a number of hours because you really need a practice run at one of your own patterns? Yeah, that might affect gauge. I can't believe how tightly that hat turned out - with super-bulky yarn on size 13s, no less! I'm almost afraid that I won't be able to replicate the relaxed, drapey feel I achieved on the last version of said hat... but I do know one thing for sure. I will definitely swatch before I cast on.