I have noticed this recently.

I'll be cruising along in a tourney, little above average stack, maybe half way through the thing. Looking good, and then suddenly get caught up in a moderately strong hand, and when i get repeatedly called, I push harder, and the villain has me beat. I lose half my stack and wonder why I didnt believe he "had It" - whatever hand "it" was I thought he was bluffing or representing.

I need to find a way to see this for what it is, but not become weak/passive either.