In Burt's estimation, what is Charlie's downfall?

In Burt's estimation, Charlie's downfall is his lack of understanding (tolerance).

"Just that you've come a long way kind of fast," he said. "You've got a superb mind now, intelligence that can't really be calculated, more knowledge absorbed by now than most people pick up in a long lifetime. But you're lopsided. You know things. You see things. But you haven't developed understanding, or-I have to use the word-tolerance. You call them phonies, but when did either of them ever claim to be perfect, or superhuman? They're ordinary people. You're the genius."