Their margin loan as the broker is protected, while the equity owned by the investor is not.

FORBES: In Volatile Market, Watch Out For Margin Calls

If an individual plans both to own shares and to borrow, he will often get a lower rate of interest on a margin loan, because it is secured against shares.

ECONOMIST: Marginal differences

Then his broker offered some advice: Cash in those options, but instead of selling some of the shares to cover the exercise price and related taxes, just take out a margin loan.

FORBES: Out of Options