On December 7, 2005, a curious thing happened in a Harvard classroom. Professor Michael D. Smith stood in front of a group of computer science students to introduce a guest speaker: entrepreneur and former Harvard student Mark Zuckerberg. What was curious was that the room was nearly empty. The class met in a huge lecture hall, but there were barely a dozen people in the room.

How could that be? Why was there so little interest in Zuckerberg’s presentation? Some explanations come to mind. First of all, Facebook was still relatively young at the time—not even two years old. And Zuckerberg himself was just 21. Even the professor wasn’t sure how to describe Facebook, calling it a “social networking program, or whatever you want to call it.”

But I don’t think that fully explains the nearly empty room. Yes, Facebook was still relatively new, but even then, its influence was growing quickly. It already had six million users across 2,000 college campuses, and it had more traffic than Google—sixty percent more—so Facebook was hardly an unknown.

The explanation, I believe is a phenomenon known as “bounded rationality.” In short, what this means is that people don’t always make rational decisions—not because they don’t want to, but because they have a limited ability to do so. There is no shortage of information all around us. What is in short supply, though, is the time that would be required to process all the information that bombards us each day.

And that is why, I believe, so many presumably smart and motivated computer science students passed up an opportunity to attend an hour-long Q&A session with someone who was well on his way to becoming a leader in their field. It’s not that they didn’t know who Zuckerberg was. It’s that they didn’t realize who he was going to be, and why it might be worthwhile to attend.

Bounded rationality also impacts our ability to make good financial decisions. Research has shown that often we get interested in things just because they happen to cross our radar. At the same time, we tend to discount or ignore things that don’t grab our attention, whether they are important or not.

How can you protect yourself from this phenomenon? Here are four ideas:

1. Each time you are considering a big financial decision, ask yourself why you want to make that particular decision. Was the idea the result of something that you just happened to hear about, or was it the result of a methodical search?

2. Recognize the implication of bounded rationality for “hot” investments, be it Tesla stock, the Contrafund or cryptocurrency. The stocks of fast-growing companies may get all the attention, but the data clearly show you’re better off with the stocks of more mature, slower-growing companies. So-called “value” stocks have outperformed “growth” stocks by a wide margin, on average, over time.

3. If you have an investment idea, and it’s not something anyone has ever heard of, don’t discount it. There’s an old joke about two economists walking down the street. Suddenly, one of them spots a $100 bill and begins to pick it up. “Don’t bother,” his colleague says. “If there were really a $100 bill, someone would have already picked it up.” The joke, of course, is that sometimes there really are opportunities that you see, or understand, before others. It may be infrequent, but it does happen. I generally recommend against picking individual stocks, but that doesn’t mean it can never work. And you shouldn’t be dissuaded just because it isn’t one that everyone’s talking about. Just be sure to keep your bets to a reasonable size.

4. When considering financial risk, look beyond the recent past and the “consensus” view among Wall Street pundits. In November 2008, in the depths of the financial crisis, Queen Elizabeth convened a group of economists and asked a simple question: Why didn’t anyone see this coming? One brave soul answered, “At every stage, someone was relying on somebody else and everyone thought they were doing the right thing.” In other words, no one was worried about a recession because no else was worried about a recession. If that sounds circular, it is. And that’s why bounded rationality is so tricky. The lesson: As you structure your finances, try to think beyond the groupthink. Just because something has never happened before, or hasn’t happened recently, or no one’s talking about it—that doesn’t mean that it can’t happen.

P.S. You can see a video of Zuckerberg’s lecture on YouTube.