are players ever just "not smart enough" to move up?

[DagnyTaggert]

I think it has more to do with nerve/guts than smarts once you hit middle/upper-middle limits. Many of us are paralyzed by thoughts of losing thousands of dollars a day and stay in our comfort zone, grinding out $1500/week or so.

The game changes significantly at the $80/160 limit and $10/20 NL level. Most players are competent at this level, the winners in those games are even more aggressive than most winners at the next level down and a losing streak does not bother them.

Winning poker does not require a great deal of intelligence, at least the way most of us define intelligence. It does require inflection, self-honesty, information, and nerve.