Take for example: you’re in your local supermarket, it’s very busy with lots of people bustling around you, and some of the items you really need are sold out. The price of coffee has gone up and the checkouts all have enormous queues. By the time you eventually get to be served the cheerful checkout girl smiles and says a chirpy hello only to have you respond with a big frown and a grunt. What happens to her? She withdraws the cheerfulness and the smile disappears. Try the opposite. Arrive at the checkout smiling and full of the joys of spring and it is likely
they will respond in the same manner.