The belief-bias effect occurs when people let their existing beliefs interfere with logical reasoning. If a conclusion fits what we already believe, we’re more likely to accept it as true—even if the logic is flawed.
For example, someone who believes exercise is always good might accept the argument “All things that are healthy require effort. Exercise requires effort. Therefore, exercise is healthy,” without noticing the faulty reasoning.
This bias shows how emotions and beliefs can overshadow pure logic. It affects everyday decision-making, debates, and even scientific reasoning. Recognising belief-bias encourages us to slow down, separate evidence from assumptions, and question whether we are agreeing with an argument because it is logical—or simply because it aligns with our existing thoughts.