Imagine you are playing with toy cars with your friend. Your friend really likes the red car and wants to play with it all the time. But you really like the blue car and want to play with it.
One day, your friend accidentally drops the red car and it breaks. You feel bad for your friend because they love the red car so much. So, you decide to give them your blue car to play with instead.
Your friend is happy to have the blue car, but they still really want the red car. They keep talking about how much they wish they had the red car instead of the blue one.
Eventually, you start to believe that the red car is better and that your friend really wants it. So, you start to act differently around your friend. You let them play with the blue car sometimes, but you also keep bringing up how great the red car is and how much your friend loves it.
Your friend notices how you act and starts to believe that the red car is better, too. They start to act like they like the red car more than the blue one, even though they still enjoy playing with both cars.
This is called behavioral confirmation. It happens when someone's beliefs or expectations about a situation cause them to behave in a way that confirms those beliefs or expectations. In this case, your friend's love for the red car made you start talking about it more, which made your friend believe it was better and act like they liked it more.