Investors make plenty of mistakes with their savings. But some mistakes are more important than others. The biggest one of all can make a huge difference to your retirement.

In the following video, Dan Caplinger, The Motley Fool's director of investment planning, talks about the one retirement mistake that can have the biggest impact on your retirement: cashing out your 401(k) plan account. Dan notes that millions of people do this when they leave jobs, paying tax and 10% penalties on the money they receive. But as Dan notes, the even bigger impact comes from not having that money growing for you to help support you in retirement. Dan concludes that for most people, rolling over old 401(k) plan accounts is a much smarter move than just taking the money and running.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.