If we include both the beauty of pain as well as the beauty of pleasure, we might ask why we speak of beauty at all. The answer is that beauty here means fullness, totality--total experience. Our life is completely full even though we might be completely bored. Boredom creates aloneness and sadness, which are also beautiful. Beauty in this sense is the total experience of things as they are.
From Ocean of Dharma: The Everyday Wisdom of Chogyam Trungpa, quote 330