the advice I got before driving was: your left hand is the one where the thumb is pointing to your right hand
and I still think about it
If you lay your hands flat with each thumb pointed at the other hand, your left hand will form an “L” shape. That’s probably what they meant to say.
Edit: oh looooooool, I literally just didn’t get the joke
This actually makes sense. I always assumed people know which one their dominant writing hand is and go from there. That’s what i always did until i just knew. Like when someone asked me, i made a fist or something with the hand i was writing with