The story of MM's. They don't have to own every share that they trade. So they are never caught having to cover in adverse conditions. Their trick is to keep selling at as high a price as they can along the way up so their average price to cover ends up being less. They will go for extended periods of time on naked short positions and wait until all the excitement dies off and then cover. Their favorite trick is a nice gap open so they can sell tons of shares at high prices at the open and once the demand stops they pull the bid back and watch it fall and then cover.