“Today is doomed to die — because yesterday died, and because tomorrow will be born.”

"Tomorrow" (1919), as translated in A Soviet Heretic : Essays by Yevgeny Zamyatin (1970) edited and translated by Mirra Ginsburg
Context: Every today is at the same time both a cradle and a shroud: a shroud for yesterday, a cradle for tomorrow. Today, yesterday, and tomorrow are equally near to one another, and equally far. They are generations, they are grandfathers, fathers, and grandsons. And grandsons invariably love and hate the fathers; the fathers invariably hate and love the grandfathers.
Today is doomed to die — because yesterday died, and because tomorrow will be born. Such is the wise and cruel law. Cruel, because it condemns to eternal dissatisfaction those who already today see the distant peaks of tomorrow; wise, because eternal dissatisfaction is the only pledge of eternal movement forward, eternal creation. He who has found his ideal today is, like Lot's wife, already turned to a pillar of salt, has already sunk into the earth and does not move ahead. The world is kept alive only by heretics: the heretic Christ, the heretic Copernicus, the heretic Tolstoy. Our symbol of faith is heresy: tomorrow is an inevitable heresy of today, which has turned into a pillar of salt, and to yesterday, which has scattered to dust. Today denies yesterday, but is a denial of denial tomorrow. This is the constant dialectic path which in a grandiose parabola sweeps the world into infinity. Yesterday, the thesis; today, the antithesis, and tomorrow, the synthesis.