After every meditation session my teacher, with his eyes still closed, would softly speak in Pali the words of the Buddha,
Sabbe sankara aniccati, yada pannaya passati, atha niggindati dukkhe, esa maggo visuddhiya. It means all conditioned things are impermanent, that when one sees this with the eye of wisdom, one becomes disenchanted with suffering. This is the path to purification. Impermanence is a good subject.
All conditioned things are physical and mental formations, all phenomena are not permanent and without self. A tree, the cell of a bacteria or animal, a star, even a thought. All of these are conditioned as they exist based on the conditions of other things. These arise, exist and pass. We should spend time understanding this impermanence.
Seeing with wisdom requires experiential knowledge. It is not through theoretical yammerings that we can understand impermanence but with applied and sustained effort through meditation and awareness. These are without base and are not reliable foundations for true happiness. This is a great source of suffering/stress (dukkha).
It is through deep investigation into the arising and falling of all conditioned things that we can understand the true nature. Seeing the truth of all impermanence as it relates to our minds during swordsmanship training and life. Do you feel permanence within and around you? What is permanent?