And even if the fox trained, there would be optimism or pessimism to the possibility to train as much as needed to jump that much higher. The optimism would be a factor in other ways too. He would think that in the future he will come across grapes and he will need to jump higher. Or he thinks that these grapes will be in the tree when he is strong enough to get up there. I don't think there is any way of removing optimism and pessimism from the picture.