When the Buddha said: "Do not pursue the past," he was telling us not to be overwhelmed by the past. He did not mean that we should stop looking at the past in order to observe it deeply. When we review the past and observe it deeply, if we are standing firmly in the present, we are not overwhelmed by it. The materials of the past which make up the present become clear when they express themselves in the present. We can learn from them. If we observe these materials deeply, we can arrive at a new understanding of them. That is called "Looking again at something old in order to learn something new."
If we know that the past also lies in the present, we understand that we are able to change the past by transforming the present. The ghosts of the past, which follow us into the present, also belong to the present moment. To observe them deeply, recognize their nature, and transform them, is to transform the past.
- Thich Nhat Hanh, Our Appointment with Life