Offer your thoughts or opinion on the input financial query or topic using your financial background.

Short an option - random assignment?
You've described the process fairly well.  It's tough to answer a question that ultimately is 'how is this fair?' It's fair in that it's part of the known risk. And for the fact that it applies to all, pretty equally. In general, this is not very common. (No, I don't have percents handy, I'm just suggesting from decades of trading it's probably occurring less than 10% of the time). Why? Because there's usually more value to the buyer in simply selling the option and using the proceeds to buy the stock. The option will have 2 components,  its intrinsic value ("in the money") and the time premium. It takes the odd combination of low-to-no time premium, but desire of the buyer to own the stock that makes the exercise desirable.