Many great yogis started by meditating on the shortness of the human life, on impermanence, and on death. Their enlightenment, their realizations, and their Dharma practice itself all came from this meditation. Their strength and ability to live an ascetic life in extremely isolated places, to practice the vast and profound subjects and attain the higher paths, to generate the incredible energy required to persevere in their practice—all these things came from reflecting deeply on the shortness of the human life, on impermanence, on death. The fact that they attained enlightenment in that lifetime was due to this very remembrance.
– Lama Zopa, Wholesome Fear