Rosa Parks didn't just happen to stumble into a great historical moment. In fact, she had a long history as an activist. This was all unusual stuff for black folks in the South at the time.
if someone were to call the stock from you, you wouldn't have to go out and buy it -- you could just deliver the stock. The great thing is it's a contract so you know what the price is going to be and there's not a lot of guessing there.