Dalai Lama Xiv said this quote

Now there are many, many people in the world, but relatively few with whom we interact, and even fewer who cause us problems. So when you come across such a chance for practicing patience and tolerance, you should treat it with gratitude. It is rare. Just as having unexpectedly found a treasure in your own house, you should be happy and grateful toward your enemy for providing you that precious opportunity. Because if you are ever to be successful in your practice of patience and tolerance, which are critical factors in counteracting negative emotions, it is due to your own efforts and also the opportunity provided by your enemy.