> If you're off, it could still crash and you could spend more money sustaining the position than you'd make.
And in Black Scholes this is called Theta Decay. In any form of short, there are maintenance costs, and maintenance costs roughly scale with the risk-free interest rate (usually assumed to be roughly the Federal Reserve's overnight lending rate)
Theta Decay is above-and-beyond the risk-free rate because you're also losing time-value. So you must always factor in the amount of time before a predicted crash: the longer it takes the more money you lose.
