The whole secret of life is to be interested in one thing profoundly and in a thousand things well.

The saying contrasts depth with breadth: a life well lived requires one central devotion—an art, vocation, cause, or relationship—pursued with sustained seriousness, while also cultivating wide-ranging curiosity about many other subjects. It praises the kind of cultivated “amateur” intelligence associated with Enlightenment sociability: being able to converse, read, and take pleasure in varied matters without becoming scattered or superficial. The “secret” is balance—anchoring identity in a profound commitment while keeping the mind porous and responsive to the world. As advice, it resists both narrow specialization and restless dilettantism, proposing instead a stable core of purpose plus expansive, humane interests.