What Are Cognitive Biases? A cognitive bias is a systematic error in thinking. It also works as a mental shortcut to making decisions or judgements. Everyone is susceptible to cognitive bias, no matter their age, gender, or cultural background. Why do cognitive biases exist? Our brains need to take in an incredible amount of information but it also wants to save as much thinking energy as possible. So, it relies on generalities or rules of thumb (also called heuristics) to help it make hard decisions fast.