A mentifact is something that is created by humans but is not actually real. It can be an idea, a belief, or a behavior. For example, some people think that money will make them happy, but money isn't actually something that can make you happy - it's just an idea or a belief that people have. Another example is how people behave in different situations - like how we act differently around our friends than we do around strangers. These behaviors are not real, but they are things that people do.