As any graduate of Alcoholics Anonymous knows, the first step to setting out on the proper path is admitting your weakness. In that spirit, I'm writing about my biggest mistake so far during this bear market. Here. Publicly. For the whole world to see.

If legendary investor Peter Lynch of Fidelity Magellan fame could educate investors by publicly admitting to holding AIG (NYSE:AIG) and Fannie Mae (NYSE:FNM) at the end of last year, what's an analyst like me got to lose?

I hope two things come of my story:

  1. Someone, somewhere out there learns something from my mistakes. Feel free to consider me a sacrificial teacher.
  2. Having studied psychological commitment and consistency in Robert Cialdini's classic work Influence: The Psychology of Persuasion, I hope that my public commitment to avoid repeating these mistakes prevents me from falling victim to them again.

Mea culpa
My greatest investing failure of the past year has been my investment in Allied Irish Banks (NYSE:AIB). To date, I'm down 88%. Not quite as big a loss as investors in casino operators Las Vegas Sands (NYSE:LVS) and MGM Mirage (NYSE:MGM) have experienced, but what consolation is a few percentage points' difference when you've lost 88%?

And yet, painful though that loss is, seeing how avoidable this was in hindsight hurts even more. Perhaps the only comforting thought is that in Warren Buffett's recent Berkshire Hathaway (NYSE:BRK-A) annual report, he writes that he also suffered a significant loss by investing in Irish banks. Some have speculated that AIB was among them. So at least I was fooled alongside a much better investor than me.

Following the crowd
My first major mistake was falling prey to social proof. I put too much weight on the research, opinions and actions of others, without thinking through my investment decision for myself, and deciding whether it made sense in my portfolio.

Prior to my purchase of AIB, it had been recommended by our Global Gains newsletter, and purchased by the team charging up our real-money Million Dollar Portfolio real-money service. Advisors in both services wrote that the stock was trading with low historical and relative multiples, a very attractive dividend yield, and a significantly undervalued price.

While they made compelling arguments, I failed to carefully evaluate whether I agreed with their assessments. And I became even more hooked as these fellow analysts also began purchasing AIB for their personal portfolios.

As a result, I also began to give in to confirmation bias -- where I sought out opinions that further confirmed my buy decision, rather than seeking a contrarian opinion that might indicate danger ahead.

Seth Jayson, co-advisor of our Motley Fool Hidden Gems newsletter service, recently shared with me that confirmation bias is one of the most common predispositions investors face. He explained that truly great investors develop an ability to honestly look at both sides of an investment thesis.

Anchoring in loose sand
As if those mistakes weren't enough, I also became anchored to the price at which each service recommended the stock. I fixated on those price points; in my mind, anything lower than their entry prices became a clear bargain.

So when AIB fell another 50% from the most recently recommended price, the stock became twice as attractive to me, as did the doubled dividend.

These mistakes fed off each other, collectively convincing me to overlook my normal investment process. I took shortcuts. I failed to perform as much research as I typically do. I fell in love with the stock, viewing it as mostly upside, without truly understanding the risks and pressure points. And I didn't even consider the possibility of a suspended dividend (which recently beset the company).

This company -- which, hurt by the falling Irish economy, recently needed to boost its construction and development loan reserves -- was much more complicated than I originally thought. Andy Cross, also co-advisor at Hidden Gems, recommended to me that investments should always pass what he calls "Einstein's razor," which dictates that an investment thesis "should be made as simple as possible, but no simpler." The complexity of AIB forced me to look to other investors, and to bypass my investment process.

Lessons learned
The key takeaways from my mistakes, then, are:

  1. While it can be helpful to look at the opinions of others, you still need to carefully consider whether you agree with their investment theses. Even if AIB had risen 88%, it still would have been a mistake for me to buy it, because I hadn't sufficiently examined the reasons for owning it. You must be able to distance yourself from the positions of people you respect.
  2. It's much better to leave a stock's price history out of your analysis, so that you're not tricked into a value trap. Companies can, and often do, change. Citigroup (NYSE:C) might have looked cheap at the start of 2008, when it was down nearly 50% from just six months earlier. But credit tightened, defaults rose, the economy worsened, and the stock fell another 87% in the months that followed.
  3. It's best to simply bypass investments that are too complex, or that you don't believe you solidly understand.

These takeaways -- and countless other investor psychology topics -- are heavily studied by Hidden Gems advisors Seth Jayson and Andy Cross as they seek out the world's top small-cap companies. That has now become an even higher priority for them, as they construct a real-money portfolio of their best small-cap ideas for our Hidden Gems newsletter service.

Not only can you see their buy guidance right now, but they're also offering you the chance to read their research so you can see if you agree with their analysis. Click here for a free guest pass -- there's no obligation to subscribe.

Fool analyst Adam J. Wiederman owns shares of both Allied Irish Banks and Berkshire Hathaway. The Motley Fool also owns shares of Allied Irish Banks, a Global Gains recommendation, and Berkshire Hathaway, an Inside Value and Stock Advisor recommendation. The Motley Fool's disclosure policy likes to learn from its mistakes.