How do you know you aren't smart?

Intelligence is not easily quantifiable (dont you dare get me started on IQ) so its pointless to worry about how you stack up in one area. Ive met a genius nurse who cant spell restaurant without spell check. I know engineers who cant visualize a 2D drawing in to 3D space. I think im pretty smart, lots of conceptual thinking comes naturally to me but I hate chess. It doesnt make sense to me. I suggest thinking about what you are good at, rather than what you're not.