Often, while I'm working, I run into a side problem, or I need to learn a small thing to get things moving. I do some research, and usually find the answer.
Later, I run into the same issue, but I can't remember exactly how I did it the first time. Sometimes, I end up doing a shorter version of the same research.
I'll try to use this diary to write down the problems I ran into, and how I solved them. Later, maybe I can remember that I ran into this issue before and just look here.