You feel cheated the moment you realise that the currency you carry is fake. You don`t know who gave it to you and even if you know the person who gave it to you, he/she is not going to take it back. Fear grips you, even though you know keeping a counterfeit accidentally is not a crime. You want to get rid of it.
You can avoid this dilemma if you know the bank notes better. Know them like the lines on your palms!