Consciousness exists on two levels: as seeds and as manifestations of these seeds. Suppose we have a seed of anger in us. When conditions are favorable, that seed may manifest as a zone of energy called anger. It is burning, and it makes us suffer a lot. It is very difficult for us to be joyful at the moment the seed of anger manifests. Every time a seed has an occasion to manifest itself, it produces new seeds of the same kind. If we are angry for five minutes, new seeds of anger are produced and deposited in the soil of our unconscious mind during those five minutes. That is why we have to be careful in selecting the kind of life we lead and the emotions we express. When I smile, the seeds of smiling and joy have come up. As long as they manifest, new seeds of smiling and joy are planted. But if I don’t practice smiling for a number of years, that seed will weaken, and I may not be able to smile anymore.
— Thich Nhat Hanh, Peace is Every Step —