Guess Why?

Dear all guild mate, guess what is the reason??? story as follow :

One day. there is a mother caterpillar, she found out that she was running out of soya sauce while cooking half way... without any choice, she ask her only son, Da Dou to out to buy immediately, coz they are having dinner very soon.
So Da Dou packed his story book immediately and getting ready to go out...
However after an hour, there is still no sign of returning of Da Dou, So his mother is furious and got a cane and thought that Da Dou went to the playground and forget about the soya sauce...
Suprisingly, Da Dou's mother saw Da Dou was loittering at the door step, so Da Dou's mother asked " Why are u here, where is my soya sauce?"
Da Dou said : I haven't go out yet.
His mother asked "why?"

So all dear guild mate, guess why???