We all have good ideas. We also all have moments that we want to remember. Both of these examples are scenarios that you want to capture.
There are lots of ways to do this. Maybe its keeping an actual journal. Perhaps taking a video or picture. It could even be writing something on your hand to trigger a more permanent recording in the near future. Regardless of what method you use, don't count on being able to recall it down the line. Capture that nugget as it might be a piece of gold.