How Smart is Too Smart?

Sometimes, I think back on books I've read where I was really annoyed with the main character. Sometimes, it was because they were too ridiculously perfect, the little "Mary Sue" protagonist and her endless talent and competency in every area. But other times, it was actually because the main character could have made some obvious choices that would've saved them from the BIG mess they eventually found themselves in. There seems to be a fine line between characters that are smart, who make good decisions and learn the art of communication in order to avoid unnecessary conflict, and characters that are just too plain stupid and incompetent. I don't have the answer to this puzzle. In fact, it is something that could be debated on a character-to-character basis. I just have to keep remembering that I've felt the frustration from both directions and keep it in mind when I sit down to write my next character to life.