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.

Don't be scared to invest
The reason why so many workers cash in their 401(k)s is that they're too scared to invest and put their money at further risk. Yet that's almost always the wrong move. In our brand-new special report, "Your Essential Guide to Start Investing Today," The Motley Fool's personal finance experts show you why investing is so important and what you need to do to get started. Click here to get your copy today -- it's absolutely free.

Dan Caplinger and The Motley Fool have no position in any of the stocks mentioned. Try any of our Foolish newsletter services free for 30 days. We Fools don't all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.