When good balls go bad

Yes, I know it's a ball.

But it's not the one I want.

I happen to know for a fact that the one I do want

is in your pocket.

No, I am not prepared to make do with this one.

And no, I am not being fussy, I am being selective.

There IS a difference you know.

Or perhaps you don't.

That would explain your inability to tell the difference between

good tennis balls and bad ones ....