You make a good point, Kalessin - maybe
Evil Defeating Itself would be more applicable to most of these cases. That certainly seems to be a very Tolkieny kind of theme, too, something along the lines of 'cheats never prosper'. Sauron and Morgoth could be cast as the prototypical Looney Tunes villain - no matter how hard they try to be evil, great good seems to spring up out of it. The bittersweet Tale of Beren and Lúthien is a fine example of how evil not only breeds courage and love through hardship, but also a ripping good yarn.
Boromir's attempt to take the Ring, Shelob's stinging of Frodo, these events were evil by nature or impulse. But Pippin's part in the books seems to be more one of
Clumsiness Defeating Itself! He does Gandalf a big favour on at least two occasions, through Tookish foolishness. I bet Merry was often left shaking his head and saying "that guy has all the luck!"
Glad to see that people are enjoying this thread by the way (even if it does veer dangerously close to the cliff of Fate vs Free Will). I hope you click on the link I provided in my first post, and also on this one on
Edward de Bono. This type of thinking has definitely changed the way I look at my life, and I'm ecstatic to find so many great examples in my favourite book.