If opportunity doesn’t knock, build a door.

The line urges proactive self-determination: rather than waiting passively for luck, permission, or external validation, one should create the conditions for advancement. “Opportunity” is personified as something that might arrive unbidden; “build a door” flips the metaphor to emphasize agency, ingenuity, and persistence—making one’s own entry point when none exists. In a broader cultural sense, the quote reflects a distinctly modern, entrepreneurial ethos: obstacles are treated as design problems, and success as something engineered through initiative. Its popularity also owes to its punchy, aphoristic structure, making it a portable maxim for career, creativity, and personal growth.