Knowing your limits has to be a sign of intelligence.

"Dumb" people (FTR the description actually refers to something rather than that which you think it does...) run around on the internet getting mad because they haven't thought things through...

It's an interesting question though. I know quite some "smart" people who lack self awareness to an almost fatal degree yet can outdo the vast majority of the population at solving logic puzzles. It tends to be a rather frustrating condition to deal with.