I occasionally do that, but most often I even forget to do that! I ought to make sure I always have paper and a pencil in my pocket so I can write stuff down as soon as it crosses my mind, so as to overcome the trivial inconvenience of having to get a pencil, which usually makes me just think “I'll write that down later” (and then forget to).
Well, the idea is to have all the things you have to do written down. (In particular, you should definitely have "making sure I have paper and a pencil in my pocket" on the list!) Do you have such a list right now? How many things are on it? If there are less than twenty, then start writing, and don't stop until you get to twenty.
Once you have all the stuff written down, you won't have to bother remembering anything; you can just look at the list.
I often feel guilty for ignoring other people's comments or questions, and frustrated when other people seem to be ignoring me. If I can't indicate to someone exactly why I'm not answering, or can't receive such an indication myself, I can at least help my future selves and others obtain a better probability distribution over such reasons. To that end, I'm listing all of the reasons I can think of for someone to not respond to a comment/question, to save the effort of regenerating these hypotheses from scratch each time and prevent the possibility of failing to consider the actual reason. Note that these are not meant to be mutually exclusive.
If I missed any reasons (that happen often enough to be worth including in this list), please give them in the comments. See also this related comment.