There is a classic story on impermanence in The Words of My Perfect Teacher. A practitioner did a retreat in a cave for nine years. At the entrance of the cave, there were some nettles. His robes always got caught by the prickly plants every time he left the cave. As it was kind of a bother, he thought about cutting the nettles. Then the thought of possibly not being able to return to the cave again crossed his mind, he decided to do something more meaningful with his time instead. When going into the cave, his robes got caught as well. The thought of removing the nettles arose again. But considering the possibility that this might be his last time leaving the cave, he decided against it and saved the time for training the mind. He continued like this for nine years until he attained accomplishment in his practice while the nettles remained standing at the entrance. It was his firm conviction that all phenomena are impermanent that made him treasure every moment of his life by not spending it on something meaningless but practicing the Dharma. His accomplishment came as the result of realizing impermanence, not emptiness, of all phenomena.

- Quote from The Right View, "The Four Noble Truths—the Path Out of Samsara"