You might be a bit surprised about this title. Isn't it obvious that one has to root for success? This question came to me when I read Vivekananda in one of his books on Vedanta. In it he claimed that he would rather be exposed to criticism than praise, just to keep the ego in check. I am not sure I am rooting for failure, but I did observe that when you are struggling a bit, you feel a resistance. You actually feel the presence of the me which is under attack and you have a glimpse at the True Self which is silently observing the me. In contrast, when you are successful, it is hard to seperate the two. You feel you are at the top of the world and you care little about the fact that while your me is at the top of the word your True Self is probably somewhere else.
There is also a big difference in energy that you experience in both states. When you experience a failure, your energy level drops and you need lots of coffee just to compensate. Instead, when you feel succcessful you are bouncy and you don't know where to go with your nervous energy. Both states are a deviation from the ideal. In the ideal you experience the same level of energy independent of the perceived state you are in. The Gita states, he who is steadfast in success as much as in failure, he is a yogi. But of course, being a yogi is easier said than done.
My conclusion on the subject is actually quite simple. Success and failure are both great learning tools for your spiritual development. Both shall pass once your lesson is learned. When I worry about the consequences of a decision, I typically say to myself: Success or failure, both have their usefulness. The I prefers success, but my True Self welcomes both states as necessary learning experiences. True Self, may your will be done.