When you hear the words lump-sum..it sounds big.   It sounds like a pension or retirement plan that could last for years. 

USAToday explains the "lump-sum illusion" and how important it is to look at our withdrawal rates from retirement plans.

As 79 million baby boomers march into retirement over the next two decades, they risk falling into a trap that Olivia Mitchell, a professor at the Wharton School of the University of Pennsylvania, calls "the lump-sum illusion."

"People look at their 401(k) sum and think, 'I have $100,000 or $1 million; I'm rich,' " Mitchell says. "The danger of the lump-sum illusion is that people don't understand how expensive it is to get old, and they withdraw too much."