Death
The most fundamental thing to be remembered is that life is dialectical. It exists through duality, it is a rhythm between opposites. You cannot be happy forever, otherwise happiness will lose all meaning. You cannot be in harmony forever, otherwise you will become unaware of the harmony. Harmony has to be followed by discord again and again, and happiness has to be followed by unhappiness. Every pleasure has its own pain, and every pain has its own pleasure.
Unless one understands this duality of existence, one remains in unnecessary misery. Accept the total, with all its agonies and all its ecstasies. Don't hanker for the impossible; don't desire that there should be only ecstasy and no agony.
Ecstasy cannot exist alone, it needs a contrast. Agony becomes the blackboard, then ecstasy becomes very clear and loud, just as in the darkness of night the stars are so bright. The darker the night, the brighter are the stars. In the day they don't disappear, they simply become invisible; you cannot see them because there is no contrast.
Think of a life without death, and it will be unendurable pain, an unendurable existence. It will be impossible to live without death.
Death defines life, gives it a kind of intensity; because life is fleeting, each moment becomes precious. If life is eternal, then who cares? One can wait for tomorrow forever -- then who will live now and here? Because tomorrow there is death, it forces you to live now and here. You have to plunge into the present moment, you have to go to its ultimate depth, because who knows, the next moment may come, may not come.
Seeing this rhythm, one is at ease, at ease with both. When unhappiness comes one welcomes it, when happiness comes one welcomes it, knowing that they are partners in the same game.
This is something which has to be continuously remembered. If it becomes a fundamental remembrance in you, your life will have a totally new flavor -- the flavor of freedom, the flavor of unclingingness, the flavor of nonattachment. Whatsoever comes, you remain still, silent, accepting.
And the person who is capable of being still, silent, accepting of pain, frustration and misery, transforms the very quality of misery itself. To him, misery also becomes a treasure; to him, even pain gives a sharpness. To him, even darkness has its own beauty, depth, infinity. To him, even death is not the end but only a beginning of something unknown.
-Osho, “The Book of Wisdom, #12, Q1”