With the unexpected punchline, you laugh with delight. Your friend is so witty. But when he repeats the joke to others, you don’t find it funny at all, and are actually quite annoyed that he would repeat it for the umpeenth time. This is a natural, human response, is it not?
But why do we laugh more and more audibly when we’re with others? Perhaps we have more control over our laughter than we truly understand. We learned how to laugh before we could talk. But if you observe human interactions around you, you’ll notice most people are laughing when there is nothing funny at all happening. According to Robert R. Provine, a professor of psychology and neuroscience at the University of Maryland Baltimore County who authored the book Laughter: a Scientific Investigation, the primary purpose of laughter could be to trigger positive feelings in other people.
We don’t laugh at the same joke twice. Then why do we cry on the same sad story again and again? Again, it has everything to do with our thoughts and beliefs. (The article on Why We Cry offers much fascinating information on the science behind our tears.) You’re crying again about something you lost, something you wish hadn’t happened, or something you long for and but cannot have. What do these things all have in common? Wanting it to be different. How will crying change it? How will sadness change things?
From the Science of People, Sadness: The Science of Why We Feel Sad and Its Surprising Benefits
Humans depend on each other to survive. Sadness is the emotion that makes us remember that fact. Young children feel sad when they are separated from their parents and it’s that sadness that prompts them to cry and/or find their parents, potentially saving their lives. As people grow older, the sadness that accompanies separation is what drives people to continuously invest in relationships.