When something big comes up, such as the need for a new car, you may be tempted to use the money in your 401k retirement plan to pay for it. This is possible, but it is not wise. For one thing, you will have to pay certain fees and penalties because you are not using the money in the way that you said you would when you started the plan. This will also mean that you will have the gratification of a new purchase quickly, but you will not have enough money to retire comfortable in the long run.