'People think about you enormously less than you think they think about you' was a really important realisation for my mental wellbeing! It's quite easy to demonstrate too, pick a random person in your life who you don't have a close relationship with and try and remember some random anecdote they mentioned a month ago.

This should be drilled into schoolchildren along with reading and writing I think, many people's teenage years are intensely stressful partially because of this false notion other people remember things you did in perfect detail.