Your brokerage can then sell the margined securities in your account to cover it. You gave them this right when you signed the agreement to open a margin account. Sometimes, too, a volatile stock can drop so rapidly that your broker will sell your shares at the worst possible time, and leave you not only shareless, but also owing them additional funds. This is where the risks of margin outweigh any benefits. Investing involves risk.
Nothing is guaranteed.
However, as smart and Foolish investors, we seek to temper as much risk as we can. Margin is one risk you don't have to take. You can simply avoid it. If you do choose to use margin, watch out. Remember the risks involved.