Life & Wisdom Quote by Robert A. Heinlein

Heinlein’s line has the brisk swagger of an engineer disguised as a novelist: a jab at armchair certainty, and a pep talk with teeth. “Theoretically impossible” isn’t aimed at real physics so much as at the bureaucratic, academic, or social reflex to treat current models as permanent borders. He’s lampooning the way “theory” gets misused as a shield for timidity: not a method for testing reality, but a credentialed way to say no.

The sentence works because it flips the prestige hierarchy. Theory is supposed to be the grown-up in the room, the thing that disciplines wishful thinking. Heinlein doesn’t discard theory; he mocks the smugness that can calcify around it. “Until it is done” turns proof into an event, a public fact that humiliates the gatekeepers. There’s also a subtle double edge: it’s not saying everything can be done, only that declarations of impossibility are often premature. The target is overconfidence, not caution.

Context matters. Heinlein came out of a 20th-century American moment when “impossible” was getting routinely embarrassed by history: powered flight, the atom, rockets, space travel, computers. As a science-fiction writer with an engineer’s bias for the workable, he treats imagination as a prototype stage, not an escape. The subtext is a cultural argument about progress: the future belongs less to the people who predict correctly than to the people willing to try, fail, iterate, and finally make prediction irrelevant.