I dont know exactly it, but I think as a child he was forced to be excluded from having friends by his parents. Like they wouldnt let him play thinking it would distract him from his studies. Judging by the parents reaction it looks like that have high expectations, and say the cliche stuff like "we just want what's best for you"
That stuff can really make you mentally unstable, and the only thing keeping him going was the demon king because he never gave up for wanted revenge on the world.
This is just my observation, there might be more to it ...
Thank you very much!
I didn't understand Gozu story. Can anyone explain to me.