Learning a new motor skill. Oooh that's hard. I was accompannying a primary school class on a field trip to a chruch for Easter (

) and my table were tasked with tying wicker crosses, which meant overlapping this material tying round itself and forming a knot - and I just COULDN'T do it. I don;t know about you but I tend to be pretty dextrous at the things I've practised (I learnt to twirl a pen through my fingers for a hobby, I could do it blindfolded now) but the step up to there is HUGE. trial and error with more error and lots of trial...
More generally, alcohol I've noticed is a big thing. I stopping drinking about seven years ago but still have the odd beer or whatever and I notice the degradation in my co-ordination almost immediately, it's lurking beneath the surface. I'm sure most people aren't as clumsy as I am after one pint.
That, and being ill. when I'm generally not with it with colds or fevers and what have you, I'll be bouncing off door frames like there's no tomorrow.
Pressure will do it. My written legibility breaks down under pressure. my writing is cognitive not automatic so loss of focus impacts directly on how clearly I form letters.
Stress and sensory overload, check those too.
Yeah, I'm just a big bundle of bumble.

"You don't get anything worth getting by pretending to know things you don't know."
~ Sam Harris.