Deception refers to the act—big or small, cruel or kind—of causing someone to believe something that is untrue. Even generally honest people practice deception; various studies show that the average person lies several times a day. Some of those lies are big (“I’ve never cheated on you!”) but more often, they are little white lies (“That dress looks fine”) deployed to avoid uncomfortable situations or spare someone's feelings.
Deception isn’t always an outward-facing act. There are also the lies people tell themselves, for reasons ranging from healthy maintenance of self-esteem to serious delusions beyond their control. While lying to oneself is generally perceived as harmful, some experts argue that certain kinds of self-deception—like believing one can accomplish a difficult goal even if evidence exists to the contrary—can have a positive effect on overall well-being.