Nothing kills the best-laid investment plans more than emotions and overconfidence. With the stock market continuing to break records, investors may be thinking a little too highly of their stock-picking abilities, but as one investing adage goes, "don't confuse brains with a bull market." That's a recipe for making costly errors, and it's not the only blind spot an investor is likely to have.

All investors have some sort of bias that, if left unchecked, can lead to poor investment decisions, says Tom Kukulski, vice president, director and senior wealth advisor at Calamos Wealth Management in suburban Chicago. “That’s where all your rigorous analysis, if you did it, goes out the window,” he says.

[See: The Fastest Ways to Lose Money in the Stock Market .]

Financial advisors say they see similar blind spots with amateur investors, but these tendencies can be overcome. These experts listed a few common investor mistakes and how to correct them.

Letting winners become losers . Financial advisors say this blind spot is affecting investors right now and can be easily remedied. Mike Piershale, president of Piershale Financial Group in suburban Chicago, says in the past couple of years large-cap stocks have done very well, but people are having a hard time selling their winners. “You’re literally pulling back the investment that’s making you all the money,” he says.

Investors made the same mistake during the dot-com bubble in 2000, adds Justin Goldstein, a plan advisory director at Bronfman Rothschild. “People saw how everything was going up and they didn’t want to miss out. Fear of missing out is significant,” he says.

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But often this year’s hot performer can be next year's underperformer, and people end up losing money because they didn’t take profits when they should have.

To remedy this, Piershale and Goldstein recommend that investors review their current asset allocation mix and rebalance their holdings as needed. Chances are, the portfolio is off its original target setting, with the stock portion likely much higher than it should be because of the market's recent gains. “Study after study shows that rebalancing keeps your money safer,” Piershale says.

Lacking a rationale for owning an investment . If there's one universal investing truth, it's that people hate to lose money, says Charles K. Bobrinskoy, a vice chairman, head of investment group and portfolio manager for the Ariel Focus Fund and Ariel Focused Value in Chicago. “As a result, humans will go to huge lengths to not incur any loss in any investment, even if that is only a small part of their overall net worth,” he says. “And even if that loss is only for a short period.”

[See: 7 ETFs for a Solid Portfolio Defense .]

That can lead to people investing too conservatively or not at all, Bobrinskoy says. To overcome this tendency, he says investors should recognize that what happens to an investment in the long run matters more than the next week or the next quarter. The trick to becoming a better long-term investor is not looking at your account too often, he says, adding that even quarterly glimpses may be too frequent. If you look too often you're bound to catch the stock market when it's down 5 percent, and "you'll just panic and sell at exactly the wrong time."

You'll be less likely to panic if you have a thesis for your investment, with a well-thought out rationale for when to buy and hold. "Until that breaks down, that’s when you sell,” Kukulski says. “Did Johnson and Johnson (NYSE: JNJ ) have a bad day or quarter? Go back to your original [rationale] and test it. Be scientific.”

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Considering only the data that reaffirms your views. People often seek data that underscores their previous thinking, a tendency known as confirmation bias . “The problem with that in investing is you need to be open to the possibility that things may change,” Bobrinskoy says. If you only look for data that already confirms your opinion, you might miss out on information that could alert you to a changing market.

The way to overcome confirmation bias is to be disciplined and to look for viewpoints that contradict your own. That's hard to do, unless the person has good self-awareness, experts say. Sometimes it’s easier to have someone play devil’s advocate, which is what Bobrinskoy's firm does when deciding on new investments. An opposite view from another person may be just what you need to gain new insight, adds Kukulski. “See if they can convince you,” he says. “If your facts hold up, go with it." At least you’ve sought out other ideas.

Ignoring your limitations. Investors who panic-sell when the market falls, even after reading their investment plan, or can’t make rational investing decisions might be better off having a financial professional invest for them.

“Know when you can’t do it yourself,” Piershale says. “If you’re too emotional, it may be time to get help.”

[See: 13 Ways to Take the Emotions Out of Investing .]

Putting retirement saving on autopilot can also reduce the chances of succumbing to emotion-based investing, Goldstein says. You're more likely to stick with a savings plan if you have money taken from your paycheck automatically each month, he says. "On the 401(k) side, it’s why provisions like auto enroll are so powerful.”

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