Montaigne isn't simply urging self-knowledge, though that's part of it—he's arguing that most people are *occupied territory*, owned by their circumstances, their social roles, the expectations others have planted in their minds. To belong to oneself means recognizing that you are not your job title, your family's disappointments, or the person you perform yourself to be at dinner parties. A person might spend decades in a respectable career, married to the right person, and still wake at sixty realizing they've never asked what *they* actually want—and that estrangement from oneself is more crippling than any external failure could be.