The aspiration to rejoice [in the good fortune of others] can feel feeble compared with our resentment or self-pity. We know how easy it is to let our emotions hook us in and shut us down. We'd be wise to question why we hold a grudge as if it were going to make us happy and ease our pain. It's rather like eating rat poison and thinking the rat will die... Whenever we get caught, it's helpful to remember the teachings-- to recall that suffering is the result of an aggressive mind. Even slight irritation causes us pain and we indulge in it. This is the time to ask, "Why am I doing this to myself again?"
--Pema Chodron, The Places That Scare You, Shambhala Publications