Why do they have these voices in their heads?
Most Helpful Girl
Mental illness, often. Illnesses like depression make people feel like that, and they can affect anyone. It's do to with brain chemistry, you don't need a 'reason' to be depressed any more than you need a reason to have asthma :/
Society at large isn't helpful; capitalism feeds on people's self hatred because if we're all scared and think we aren't good enough we'll keep buying things to try and feel better and correct perceived flaws. Also the focus on sex and romance as the be-all and end-all of existence has the side effect that we tend to value ourselves based on the opinions of others and how we're treated.
On a more micro scale, abuse of any kind can cause a lot of emotional damage. People who've suffered abuse are often manipulated by their abuser (s) into thinking they deserve it, and that can really fuck up someone's self worth :(
I hope you're okay asker. You are important and deserve to feel good about yourself <30
Most Helpful Guy
It's easy to compare ourselves to others but you don't know the story. You don't know what that other person with the "perfect" life is going through, and you don't know how many filters that girl on Instagram ran her selfie through in order to look that perfect. That's why you just compete against yourself.1