My family in London

A wise man once sat in the audience & cracked a joke.
All laughed like crazy. After a moment he cracked the same joke again and a little less people laughed this time. He cracked the same joke again & again, when there was no laughter in the crowd,  he smiled and said,
"When you can't laugh on the same joke again & again, then why do you keep crying over the same thing over and over again”