Law of small numbers
In Negotiation, Lewicki, Saunders, and Barry look at the bias of the "law of small numbers." I think this is an important bias for testers to be aware of. Decision theory indicates that people have a tendency to draw conclusions from small sample sizes. The book Freakonomics hits on this several times. “This fallacy results in a tendency to believe that a small sequence of events is representative, while ignoring base rate data from a larger universe of events.”
As testers, we often interact with an applicaiton in many ways that the larger population won't. We find possible issues, and then we're asked to draw conclusions. It can be easy to believe our experiences while looking for problems might be representative of the bigger picture. Likely, they aren't. It doesn't mean they are never representative, but we need to remember to account for the big picture when we provide our feedback.
As testers, we often interact with an applicaiton in many ways that the larger population won't. We find possible issues, and then we're asked to draw conclusions. It can be easy to believe our experiences while looking for problems might be representative of the bigger picture. Likely, they aren't. It doesn't mean they are never representative, but we need to remember to account for the big picture when we provide our feedback.