Gertrude Stein:

One plunges here and there with energy and misdirection during the storm and stress of the making of a personality until at last we reach the twenty-ninth year the straight and narrow gateway of maturity and life which was all uproar and confusion narrows down to form and purpose and we exchange a great dim possibility for a small hard reality.”

Keeping open a great dim possibility, and thus avoiding a narrowing to a small hard reality, is the main purpose of life.