Falsity may exist in the perceiver or in the object perceived. In the perceiver it arises from errors in sense interpretation, unconscious expectation and bias, and, ultimately, incorrect or partial reasoning to a conclusion. Objects, human activities and events and the like may bear false appearances, by intent or by accident.
In diplomacy falsity may be the instrument to gain advantage: for example, the pro-Hitler non-aggression pact. In politics falsity may be employed in promises or in allegations concerning opponents. Optical illusions illustrate falsity in sense data. Supernatural phenomena, sightings of monsters and unidentified flying objects may be false perceptions. Overly-optimistic and overly-pessimistic outlooks falsify probable outcome anticipations. Polite behaviour may be an inculcation to practise falsification. Several crimes involve falsity: impersonation, signature forgery, hoaxes, currency counterfeiting, art forgery, 'confidence rackets', fraudulent claims for products, false arrest and, in some jurisdictions, transvestism.
The wise are pleased when they discover falsehood.