A belief is a thought about how things are – about what really is or is not the case. For instance, someone who believes in God believes that a being such as God actually exists. Assuming that people would prefer to have true beliefs rather than false ones, then they need to find a way to determine which is which. Unfortunately, people have a tendency to want to ‘protect’ their existing beliefs by only seeking evidence that supports them and being blind to contrary evidence. This makes for a very poor test of whether a given belief is indeed true. Actively seeking the evidence that goes against your own beliefs allows you to make a proper assessment, and consequently a far more reliable judgment.