The Lifespan of a Human Being: A Single Breath

The Buddha asked a monk, "How long is the human lifespan?" The monk replied, "It is but a few days." The Buddha said, "You have not yet understood the Path."

He asked another monk, "How long is the human lifespan?" The reply was, "It is the time required for a single meal." The Buddha said, "You have not yet understood the Path."

He asked a third monk, "How long is the human lifespan?" The monk replied, "It is the time it takes to inhale and exhale a single breath." The Buddha said, "Excellent! You have understood the Path."

from Section 38 of "The Sutra in Forty-Two Sections Spoken by the Buddha"

Don't cling to the past and future, but live in the present world. One must understand "now" and observe all beautiful things.