I am a note taker. I have to be. If I don't write down something I'll need to remember later, invariably I'll forget, or spend a few minutes trying to remember.
One of my friends would tease me about my getting older and that I can't remember stuff, but I think I've always had the problem. If I don't write it down, I'll forget and be disappointed in myself because I forgot something that could have been wonderful to remember. Whether it's grocery lists, appointments, meetings, or story notes, I may, at first, think it's dumb I should write something down-sure I'll remember it later, it's so simple-but ten minutes later walking the isles with five out of the six items in my basket ready to go, I'll stand there in the middle of the food store like I'm an alien plunked down into one of Earth's strange cultural establishments, staring off into the distance like E.T. wanting to go home...and wanting to be home because I can't remember the sixth item. And if I then shrug my shoulders and think I'll get it next time...when I get home, it's the one item I really needed to make the next meal.
How many great ideas have I forgotten for stories or little tidbits have I wanted to include but didn't because I didn't write them down at the time I thought of them? I don't know, I can't remember.
I am getting better, though. Slowly, in incremental steps. Yes, I still forget to note down grocery items, but story ideas and extra bits I usually get down on paper. The problem I run into afterwards is making sure I remember to refer back to the notes when the time comes to write the particular scene. Normally, it's not too difficult to add the bit in if I did forget the first time around.
When I do research and am obtaining information from someone regarding a particular subject, or jotting down descriptions of scenery, I'll write down far more than what I'll use in the story. But that's ok, because I'd rather have too much than not enough and come off sounding as if I didn't do my homework.
Filing is also a problem. Well, filing is not the REAL problem, space is. My apartment is too small to have all of my writing papers in their own slots.
Currently my filing system is composed of about five large piles with-hopefully-the unimportant or past stuff on the bottom and the current stuff, or stuff I think I want to get back to soon, on top. And those little notes? Well, that would take an excavation team to sort through those or to even find them in the first place.
Of course, it's important for us writers to be organized, in our own fashion, but that's the nature of the beast and we all have our own methods of dealing with filing and note taking. If you can be meticulous, great. If you're a piler-if I can create a word here-then don't whine when you can't find something.
Either way, please don't rely on your memory; you have too much else going on to try to remember that cool little factoid to include.
Write it down!