Consider the following fable:
A Fox one day spied a beautiful bunch of ripe grapes hanging from a vine trained along the branches of a tree. The grapes seemed ready to burst with juice, and the Fox's mouth watered as he gazed longingly at them.
The bunch hung from a high branch, and the Fox had to jump for it. The first time he jumped he missed it by a long way. So he walked off a short distance and took a running leap at it, only to fall short once more. Again and again, he tried but in vain.
Now he sat down and looked at the grapes in disgust.
What a fool I am, he said. Here I am wearing myself out to get a bunch of sour grapes that are not worth gaping for.
And off he walked very, very scornfully.
What is the theme of this fable?