“I want to reiterate that the “textbook definition” of delta has nothing to do with the probability of options finishing in- or out-of-the-money. Again, delta is simply the amount an option price will move based on a $1 change in the underlying stock. But looking at delta as the probability an option will finish in-the-money is a pretty nifty way to think about it. And if there’s one thing I want to encourage in this playbook, it’s nifty ways of thinking about options.”