Ideas pop in and out of existence unexpectedly, that’s my experience at least. This one professor from college always comes to mind when an idea is lost because I failed to write it down. He spent a few classes discussing with us some productivity/time management methods like Get Things Done, Eisenhower Matrix and others.
Writing it down, and more specifically: (1) what needs to get done, (2) when should it be taken care of (or revisited next), and (3) get it done. This is an oversimplified (butchered?) version that happens to work for me, but at least I’ve felt a boost in productivity since using it.
The tool that I enjoy using the most is Apple’s Reminders. The integration feels great, after Catalina came out at least. It gives me the flexibility I need in order to run my own Frankenstein method.
I’m not endorsing/evangelizing any of the methods/techniques out there, I’m only taking note about how having any system in place has felt empowering compared to keeping nothing other than mental notes.