Loan sharks are bad because they charge very high interest rates on the money they lend. This means that if you borrow money from them, you will have to pay back much more money than you borrowed. They also often use mean and scary ways to get the money back if you can't pay them on time, which can be very scary and upsetting. It's better to borrow from a bank or credit union, where the interest rates are lower and they are more understanding if you have trouble paying back the loan.