Ocular dominance

There are a bunch of methods to determine this: https://en.wikipedia.org/wiki/Ocular_dominance#Determination

The one my dad showed me as a kid is the one I usually show others: The Porta test. The observer extends one arm, then with both eyes open aligns the thumb or index finger with a distant object. The observer then alternates closing the eyes...

It meant that as a right hander with left eye dominance, I started shooting pool left handed at a young age. I don't think it's had much importance otherwise, though.

Thinking more about it, I think when I do shoot right handed, or if I always would have, I'd just need to keep the left eye closed ahead of time -- to avoid the shift that occurs once closing it, having already aimed.