You nailed it.

Playing too many hands.

Odds, betting amounts, and position are extremley impotant, but if you are playing too many hands then you can cancel out any possible edge you have when taking advantage of these other aspects. Sure it is all relative, you should be playing a lot of hands in position and sure you could pick up a lot of pots by betting crazy large amounts, but eventually you will just get caught to much to make your odds plays count and your reads matter. If you play too many hands you are simply setting yourself up to fail way too often, cancelling out any other small edges you may gain from position and knowing your odds.