Courage. no matter how much power you have, you can still be cowardly, and no matter how wise you are, you still may not have the guts to accomplish your goal. You can gain, if you don't already have a high level of intellect, which implies to some degree that you are able to apply your knowledge, even if it is not to the level that the triforce of wisdom gives you. Power can be gained to some degree by training, technique, and a sharp mind, though again, not to the level of the triforce of power. The true problem is that you can't use any of them to their fullest extent without the others.