Word/term of the day: Executive dysfunction,
When there's something you know you should do, it needs to get done, you want to do it and are thinking about it, you even feel bad for not doing it, but you mentally cannot get yourself to start the task and the guilt only makes it worse, so you subconsciously start doing literally anything else to distract yourself.
(it's an actual mental condition and far more complex but this is super common with it and EVERYONE has experienced this at least once im pretty sure.)