To know how to grow old is the masterwork of wisdom, and one of the most difficult chapters in the great art of living.

This remark is generally attributed to Henri-Frédéric Amiel in connection with the posthumously published selections from his private journal, a work in which he repeatedly reflects on self-cultivation, resignation, and the moral psychology of everyday life. The line fits Amiel’s late, introspective preoccupations: how to meet time’s losses—diminishing strength, narrowing horizons, and the approach of death—without bitterness or self-deception. In the journal’s aphoristic mode, “growing old” is treated less as a biological process than as a spiritual and ethical task, one that tests whether a person can convert experience into serenity and proportion rather than regret.

Amiel frames aging not as a passive biological process but as a demanding ethical and psychological practice. “To know how to grow old” implies learning the disciplines of perspective, acceptance, and detachment—without surrendering vitality of mind. Calling it the “masterwork of wisdom” suggests that the culmination of a thoughtful life is not brilliance or success but the ability to meet decline, loss, and limitation with composure and meaning. The phrase “one of the most difficult chapters” underscores that this is learned late, under pressure, and often imperfectly. The quote elevates aging into a final test of the “art of living,” where character is revealed in how one inhabits time’s narrowing horizons.