It used to be thought that we are the only species which can deceive at will, but then some clever zoologists noticed that other ones do it too. Apes who hide bananas for examples, and birds that don’t fly straight to their nest, but land somewhere else and walk home, to trick their enemies.
Evolution has developed deceptions too, like animals that can change their appearance to dogs that appear to be awake when they are asleep (some breeds have a lighter coloured spot in their eyebrows, supposedly so that they’ll appear to be awake when their eyes are closed).
We already know that humans are artful deceivers, but appearances are not always what they seem. Behaviour which appears to be false or untrue might be the opposite. For example, a white lie that protects another person’s dignity, or deliberately losing a game to give a child a chance to ‘win’.
Appearances can deceive, in which case the ‘deception’ is a figment of our imagination and we are deceiving ourselves without knowing it. One way round this is to ask “If”, as in “If the reason I’ve come up with couldn’t exist, what other explanations might there be?”