Markets can remain irrational longer than you can remain solvent.

The line is a caution to traders and investors: even if you believe prices are “wrong” relative to fundamentals, the market can stay mispriced for a long time, and leverage or short positions can force you out before you are proven right. It highlights the difference between being correct in theory and surviving in practice—liquidity, margin requirements, and interim losses matter. The quote is often invoked to argue for risk management (position sizing, stop-losses, diversification) and humility about timing. It also underscores Keynes’s broader insight that markets are driven not only by rational valuation but by psychology, conventions, and waves of sentiment that can dominate for extended periods.

Markets can stay irrational longer than you can stay solvent.
The market can remain irrational longer than you can remain solvent.
Markets can remain irrational longer than investors can remain solvent.