Changing Lanes

Why do people believe that if one day if they laugh too much, they will cry the very next day. Its like destiny they say. Weird I would say. How can you make such a prediction. Its like they want to cry the next day just to keep the balance of laughter & tears in their life. They say that they have experienced it in their lives. But don't humans have the tendency to forget all those good experiences as compared to the bad ones & not everyday can be a wonderful cheerful day, their are ups & downs in life for everyone. So isn't it a little too pessimistic to assume that no two days can a person laugh his heart out. Be optimistic is all I get from them being the greatest pessimist they have known but then why do they take this approach. Its all too confusing & irritating. I think its all a mental block embedded into people's mind. Why think of tomorrow when today is so full of laughter...sheesh..