weird question for the day

how do you stop yourself during the day to write down ideas? even just bullet point ideas?
i'm finding this to be the hardest thing to bring into a routine of some sort and i don't know why. i've never been a day planner kind of person, everything just kind of sticks in my head. but i know that all of these fleeting ideas that i have aren't always going to stick and i WANT to write them down, i just don't do it.

i have the notebook and everything, just waiting to be used.