When I lived in the mountains of Utah, I used to ski in the backcountry often. This is not resort skiing, and there is no patrol checking for avalanche risk, so assessing that risk becomes your own responsibility. It is an imprecise science, and there is always a chance you’ll get it wrong.

But the more my friends and I skied, the more certain we were of our ability to get it right. Here’s what happened over and over again:

1. We’d get to a slope, assess the risk and decide to ski.

2. We’d get to the bottom safe and sound.

3. We’d pat ourselves on the back for being so good at judging avalanche danger.

4. Repeat.

You don’t have to know much about backcountry skiing to imagine how dangerous a feedback loop like this can be. We were attributing a positive outcome to our skill, when it just as likely could have been (and probably was) luck.

Skiing isn’t the only place I’ve seen this kind of feedback loop. It also shows up in investing. Here’s how it tends to play out:

1. John Doe reads one whole book about Warren Buffett and decides he is an amazing investor.

2. After that extensive round of research, he buys a handful of stocks on a hot tip from his golfing buddy.