The Malkovich Bias
People who skim believe everyone else does too. People who skip over ads can't believe anyone looks at, or even clicks on them. People who search can't believe others don't.
It's such an irrational behavior that psychologists should add it to their known list of cognitive biases. I suggest they call it the Malkovich Bias - and define it as "the tendency to believe that everyone uses the web as you do."
The Malkovich Bias is especially prevalent in design and product development processes. It's usually an ugly and frustrating experience. Odds are good that you and your teammates don't use the web in the same way. So you've had conversations like...
"That needs to go above the fold because no one scrolls."
"That's nonsense. People scroll all the time. I do it on Google all the time."
"You might, but 78% of people don't." (I've actually seen someone reference made up stats on numerous occasions).
Rationally we can all accept that people are different and their approaches to the web differ, but that rational thought can be super tough to internalize.
Which is why I love usability testing. Much like traveling in a foreign country, we often witness behavior so counter to our own, that it makes us question our own dogmas. Similarly watching someone use the web in the exact opposite way we do, confronts and shakes our Malcovich Bias.
In a team setting, usability testing shakes the Malkovich Bias in profound ways. User testing shifts the debate. If a team witnesses a user struggle through something, everyone has a shared experience and understanding of that user's experience which serves as the starting point of the discussion and the eventual solution.