The tricky bit about composition (both in pictures and music) is that if you follow all the rules to the letter, you will end up with excruciatingly boring results. Deviations, breakage, mistakes and other innovations are the true subject of art. The rest is just the stage setting.
No, really. If you see a rose bush full of perfect flowers and in their midst one deformed, discoloured bloom, what are you going to look at?
Johann Sebastian Bach might serve both as the perfect antithesis to my claim and its corollary. Baroque music culminated in the spotless perfection of his works, which are indeed a marvel to behold. And still, they did not launch a tradition, they ended it. Composers veered off as far as possible. Therefore I claim: Art abhors perfection.