The halo effect is a phenomenon where our overall impression of a person, product, or entity influences how we feel about their various characteristics, often without any logical basis. Essentially, if we like one particular aspect of something, we tend to have a favorable view of everything else related to it. For example, if users find an app visually appealing the first time they use it, they might overlook minor usability issues because their initial positive impression creates a "halo" that makes everything else about the app seem better.

Conversely, if their first interaction is negative, they might continue to view the app negatively, even if it improves. This is called the horn effect and it shows how powerful and lasting a first impression can be in shaping user perceptions.