Ask HN: What are you continually forgetting?

Once every two months or so I need to look up or test in a console window whether javascript's Array.slice() method mutates the original array. Partly because I only occasionally program these days and partly because I'm not too bright, the same pattern repeats itself with a large amount of similar technical information - cmd line options, emmit expansions, etc. Are others conscious of the same pain? What specific regularly-referenced information is stubbornly stuck on the tip of your tongue? (disclaimer: I'm working on a tool to address this.) : it does not