What follows is my answer to a question posed on Quora: What was Ayn Rand Wrong About?
On the technical side of things, Rand was wrong about (1) the need to validate man’s knowledge—i.e., foundationalism; (2) that concepts require definitions and that definitions can be true or false; (3) that emotions are automatic effects of man’s value premises; (4) that abstract philosophy determines the course of history; (5) and that emotions are not “tools of cognition.” If we wished to really get into the philosophical weeds, we could probably ferret out even more technical errors, but beyond a few hard-core Rand acolytes, I doubt that anyone really cares about any of these largely technical issues. Nowadays Rand is mostly known for her zealous affirmations of egoism, “selfishness,” and laissez-faire capitalism, and her concomitant denunciations of altruism and all forms of government interventionism. Perhaps her most influential contention is that freedom and capitalism require a moral foundation, by which she meant: convincing philosophical arguments on their behalf. This conviction is based, however, on faulty assumptions about moral philosophy, human reason and psychological motivation.