What was “half the battle” in getting Colin well?

Half the battle in getting Colin well was getting him emotionally ready. Colin believed he'd spend his life in the wheelchair and viewed recovery as hopeless. Thus, he never tried.

Colin flushed triumphantly. He had made himself believe that he was going to get well, which was really more than half the battle, if he had been aware of it. And the thought which stimulated him more than any other was this imagining what his father would look like when he saw that he had a son who was as straight and strong as other fathers' sons.