"Today we feel good because things are going well; tomorrow we feel the opposite. Where did that good feeling go? New influences took us over as circumstances changed: We are impermanent, the influences are impermanent, and there is nothing solid or lasting anywhere that we can point to. What could be more unpredictable than our thoughts and emotions: do you have any idea what you are going to think or feel next? Our mind, in fact, is as empty, as impermanent, and as transient as a dream. Look at a thought: It comes, it stays, and it goes. The past is past, the future not yet risen, and even the present thought, as we experience it, becomes the past."
Sogyal Rinpoche from The Tibetan Book of Living and Dying, (27)