Pros fess up to their retirement-building blunders

— -- We all make mistakes. But when they involve retirement, serious mistakes can mean working till you drop instead of retiring in style. Invest too conservatively? You could fall short of cash in retirement. Too aggressively? A market downturn could wipe out your savings.

And here's a sobering thought: Even financial professionals — people who are paid for the wisdom of their judgments — commit financial blunders they live to regret. USA TODAY asked several experts to reveal their most regrettable financial decisions. Some of their errors led to huge losses.

Still, their experiences show that most financial mistakes aren't fatal to your retirement, as long as you learn from them. One common refrain: Start investing, carefully, as early in life as possible. And keep it up.

"If you can invest well, you don't need to save nearly as much for retirement," says Mark Zandi, chief economist at Moody's Economy.com. "And if you invest early, you won't have to save as much over your lifetime."

Here's a look at some of the mistakes the pros say they made and what they could have done differently:

Mark Zandi

Chief economist at Moody's Economy.com

Biggest mistake:Letting savings languish.

Zandi says he treated his investments with "extreme benign neglect" throughout his 20s and 30s.

"I think I saved reasonably well, but I spent no time or thought on how to invest those savings," he says. "So, consequently, my savings ended up in low-yielding cash instruments. I really did not invest in stocks or bonds or real estate.

"I was barely keeping pace with inflation, which I think is a very significant mistake because of the power of compounding," Zandi says. "I gave up a lot of potential return in the '90s. But I was taking a lot of risk in other aspects of my life, because I was starting a business. All my energy and waking hours were focused on that.

"I don't think many of us get any kind of formal training in personal finance. At least I didn't. The only training I got was that I just watched my father do the bills."

What he would have done differently:

"I should have put my money on autopilot and automatically transferred money from my checking account into a plain-vanilla stock index fund," Zandi says. "I would have gotten some diversity, but I wouldn't have had to spend a lot of time on it."

Zandi says the experience taught him the importance of educating his three children about investing. "They are old enough to make it fun and interesting," he says. "Even as simple as opening a very small account to trade stock.

"It's just a matter of commitment and discipline and spending the time. The way I think about it now is: Managing your personal finances is a daily affair. It's like brushing your teeth."

Sheryl Garrett

Founder of Garrett Planning Network, a network of fee-only financial planners for middle-income consumers

Biggest mistake:Investing in timeshares.

Garrett bought her first Florida timeshare in the early 1990s, while vacationing in Orlando. At the time, she was 26 and didn't have much of a nest egg. She attended the timeshare company's 90-minute presentation for the freebies — breakfast, $50 in cash and tickets to Universal Studios — convinced she could resist the sales pitch. But once she got there, she says, "All the language the salespeople used to sell a timeshare worked perfectly on me."