"Black-Scholes works for short-term options, but if it's a long-term option and you think you know something [about the underlying asset], it's insane to use Black-Scholes."

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Beware leverage in all its forms. Borrowers - individual, corporate, or government - should always match fund their liabilities against the duration of their assets. Borrowers must always remember that capital markets can be extremely fickle, and that it is never safe to assume a maturing loan can be rolled over. Even if you are unleveraged, the leverage employed by others can drive dramatic price and valuation swings; sudden unavailability of leverage in the economy may trigger an economic downturn.

— Seth Klarman