Let's admit it, us developers aren't well known for documenting work. We get wrapped up in the mess of the task and we tend to forget to go back to our project and add proper notes on how we built things. That's why commenting in your lines of code is so important. But what about full project builds instead of individual files? I can't remember how many hours I have spend working on the current version of my website. Do you remember? Probably not.
How many sites did you visit and utilize helpful information that got you those "ah-ha!" moments? Were they helpful blogs, Stack Overflow pages, video tutorials, etc.? Think of it as a citation for a book, only this is for your website. Most of the time when I search for questions online I not only save the links to the sources but I also save the search key word terms from search engines. I find it helpful to not always have to repeat the same questions over and over again.