One more thing which got triggered, regarding the "why shou…

One more thing which got triggered, regarding the "why should someone keep some random information for free": it reminded me of "triggers" which I experienced myself many times over and over. Stuff, which I actually didn't like and which I "overheard" or read somewhere but which I wished I could have "deleted out of my memory" but couldn't.
Sometimes "ideas/concepts/information is living rent free in my head even though I may dislike it...
The question is: what characteristics does those data have, that I/we keep it stored in our minds for free, even though we may dislike it?