Who is playing with you

I would like to start a question that if there are 25 people in a room, what the probability of two people sharing their birthday. What is your answer? The correct answer is above 0.5. Generally the people who ask this question expect that the answer they will get is lower than the correct answer. However, since this is a very famous question, if people ask the others who are familiar with the question, the answer they will get is going to be correct or very close to the correct answer; under such circumstance, people do not get the answers they expect. Therefore, to get what you want is dependent of who you are dealing with.

Sometimes people ask some questions to economists, they might feel economists act selfishly to some extend. However, this does not mean some economists are selfish, it is just about the way of how economists think questions, economists tend to think questions from the economics prospectives.

In the real world, sometimes people are thinking about who they are dealing with are the ordinary people or always the same group of people who share similar characteristics, especially when they are dealing with people who they are not familiar with; however, this is not true.

Overall, when people are dealing with the others who share some specific characteristics, they should expect that the outcome will drift away from the outcome they expect when dealing with randomly selected people whose characteristics are not special and match the mean of the entire population.