Even if a lender doesn't immediately charge you a fee if you miss a payment, you're still responsible for paying off the loan. If your payment is more than 30 days late, your loan could be considered in default. Defaulting on a loan can carry severe consequences; your credit history will suffer, your credit score will plunge -- as much as 100 points per late payment -- and you'll be far less likely to get another loan in the future.
If you continually miss payments, a lender can sell your debt to a collection agency that may charge its own fees and aggressively pursue you through emails and phone calls. Ultimately, a lender can take you to court to seek reparations if you don't remedy the situation. Be careful, make your payments promptly and don't borrow money that you can't pay back.