So, Suiboku:
beated all the adults in his village to deah
Destroyed his hometown
Killed his senior disciple who is like a big brother to him ( well, Fuukei was kinda lost it after all, and if he didn't do it he will likely be killed by Pandora )
Destroyed a lot of kingdoms
No wonder he feel like shit.
I think sage art is more about the mind than talent. You need to have a strong mind to endure all the time and dedicate yourself to training for such a long time that normal people can't even imagine. Like cultivation in xianxia novel.