There are lots of stupid things that rich people do, and a recent survey found one that -- if you did it yourself -- could ruin your chances for a comfortable retirement.

The survey was conducted by Fidelity, and it asked millionaires from generations X and Y what some of their investment patterns were. Generally, these two generations span from 1965 to 2004 -- a huge range. This means that the millionaires Fidelity talked to were likely between the ages of 21 and 49.

Fidelity found that the average millionaire of this age made 30 investment trades per month. That's an astounding 360 trades per year. This triple-whammy of investment stupidity means that these millionaires are kissing their fortunes goodbye and making it highly unlikely that they'll be able to continue the same kind of lifestyle once they hit retirement age.

In the slideshow below, you'll see how such an approach results in higher transaction costs, higher taxes, and lower overall returns. And I'll show you one super-simple strategy that can lead to much better investing.

Brian Stoffel has no position in any stocks mentioned. The Motley Fool has no position in any of the stocks mentioned. Try any of our Foolish newsletter services free for 30 days. We Fools may not 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.