Why Do Some People Have to be So Negative?

Sometimes I have a problem
Usually it is with some peoples negativity
Then again, sometimes I just have a problem
But it is my problem and I'll keep it to myself
Although some might find my attitude to be selfish
I believe it is more a case of being considerate
Because who likes to hear others complain
Or even worse, share a bellyache
So I just keep my problems
Guarded in my mind
All to myself
Which takes me back
To why some people have to be so negative
I just don't understand why they can't keep it to themselves?