As a piece of sculpture, Michelangelo's Pieta is all wrong. Of the two people it depicts, the face of one is not visible, the other looks a couple of decades younger than she actually is. The proportions do not quite make sense- a real man could not have fitted onto a woman's lap in quite the way he does. But, the Pieta is also the single most beautiful piece of religious sculpture I have seen.
Most of the time, you have to follow the rules. But sometimes, you have to just follow your heart.... after making peace with the rules.