NEW YORK (CNN/Money) – Have you ever held onto stocks for sentimental reasons and lost money as a result? Or bought something even though you could get it more cheaply someplace else?

Or did you ever let a few years go by when you didn't save for retirement even though you had the means?

Well, I have.

No one is immune from making financial mistakes. But there are honest mistakes born of inexperience and what I consider "voluntary" mistakes born of willfulness or neglect. These happen when you choose to keep your head in the sand or let your emotions drive your money decisions.

Having learned the hard way, I can say with confidence it certainly pays to crack down on the voluntary variety.

Here are a few typical dumb moves financial experts see smart people making again and again.

"I like getting refunds." I caught up with tax pro Barbara Steinmetz on April 15. Before I even told her why I was calling she could barely contain her exasperation with clients who were getting up to $10,000 refunds and glad about it. Her pleas to have them adjust their W-4s so they'd have less withheld are usually met with responses like, "But it's my vacation money."

"They consider it forced savings," said Steinmetz, also a certified financial planner. Trying to tell them they're giving the government an interest-free loan falls on deaf ears.

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If you're a refund-lover, you may think you won't be disciplined about saving the money on your own. But people who don't trust their ability to save, Steinmetz said, "don't realize they let their money and their bills control them."

"Whatever. I'll worry about the details later." One of Steinmetz's young clients took $50,000 in early distributions (withdrawals, not loans) from his 401(k) and IRA because he thought he could do so without penalty or tax if he was buying a home.

Nice theory, but wrong. You can take a distribution from your IRA for up to $10,000 without penalty if you're a first-time home buyer but you'll still owe income tax. Anything above $10,000 and you'll owe income tax and a 10 percent penalty. With a 401(k), you'll owe tax and penalty on the whole amount.

Long story short: The guy got slammed with a $19,000 tax bill, all because he didn't run the numbers and check the rules.

"I know this company." It's smart to invest in what you know. It's dumb to invest too much in any one thing just because you know it well. For instance, "physicians just love pharmaceutical stocks. They'll buy too much (of the sector)," said certified financial planner Chris Cordaro.

Employees also continue to own too much company stock because they're overconfident they'll know when something is about to turn bad, he said.

Cordaro's advice? Don't invest more than 10 percent of your money in one stock or more than 30 percent in one sector.

"I'm not contributing to my 401(k) in this market." Good for you. Now you're depriving yourself of tax-deferred savings for the future, a present-day tax break and, if your employer matches contributions, free money.

Moreover, Steinmetz asked, since when did contributing to a 401(k) mean having to invest in stocks? If you're truly allergic to risk, stick your plan contributions in a low-risk bond or money market fund until you get your courage back.

"No way am I contributing to a non-deductible IRA. There's no tax deduction." Oh, brilliant. Because, after all, what good are IRAs without the deduction?

Well, let's see. There's the little issue of your future not funding itself. Unless you set aside enough money, tax deductible or not, your later years will be a lot less golden.

And money in a non-deductible IRA grows tax-deferred. That means it can grow faster than it might in one of your taxable accounts, where you'll pay taxes every year on dividends, capital gains and interest to Uncle Sam and your state.

"After the experience I had, I'm not doing that again." It's human nature to project your recent experiences into the future, Cordaro said.

Take the late 1990s. Shareholders saw record growth in stock prices and projected that kind of growth in their long-term portfolios. Now after three years of a bear market some are projecting negative returns going forward and they want out.

Both perspectives are understandable but distorted, he said. The key is to catch yourself before making big moves based on these distortions and to adopt a disciplined, balanced plan that keeps you on track through good times and bad.

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"Just put it on my credit card." If your Visa gets more exercise than you do, you may justify the workouts by telling yourself you're getting miles for your purchases or an interest-free loan until your bill comes due.

That may be true. But admit it, isn't it a little easier to spend what you don't have when you trip the plastic fantastic?

"Cash is a conscious thing," Steinmetz said. That is, you're less likely to be so free with your money if you're constantly handing out $50 bills when the urge to buy strikes.

"I know I should refi, but it's such a hassle." Your time is money and you just don't want to bother with the paperwork.

Well, Steinmetz argued, suppose you can save $3,600 a year with a refi, as was the case for one of her clients. And say the refi process takes 10 hours. "How many people are paid $360 an hour?" she asked.

Bottom line: the time it takes to refinance may pay you more than you could make otherwise.

Jeanne Sahadi writes about personal finance for CNN/Money. She also appears regularly on CNNfn's "Your Money," which airs weeknights at 5 p.m. For comments on this column or suggestions for future ones, please e-mail her at everydaymoney@cnnmoney.com.