Ask HN: How do you use the knowledge gained in a day?

I'm paraphrasing yesterday's Ask HN post: https://news.ycombinator.com/item?id=43976045

Every time I see posts like this, I feel like I should take more notes. I do write some down, but I rarely use them afterward.

I'm curious, what do you actually do with your notes? How do they help you in real life?