A fundamental-attribution error is when you assume that the actions someone takes are a direct reflection of who they are as a person rather than the scenario they were in. In reality, it is more likely that someone’s actions reflect the circumstances rather than who they are.
An example of this is if someone shows up late to a first date. If the fundamental-attribution error is applied, one might assume that the date is rude and doesn’t respect your time. What is statistically more likely is that, despite the person’s best efforts, they ran into traffic or had something come up unexpectedly.