In my first flying job we had one guy who came to us with a CPL. I had to endorse him on a couple of the single-engine aircraft in the fleet, because in those days each type required a separate endo. He was hopeless and I told the boss this. Anyway, after damaging one aircraft and writing off another he was 'let go' as the Yanks say.
His wife was in tears. Although I was very young myself and not trained to deal with this type of situation, I gently told her that perhaps she should encourage her man to take up Air Traffic Control if he wanted to stay close to aviation.
Anyway, to cut a long story short, a few years later he killed himself and a few others - in a twin.
There are a few people who just don't have it and will never have it no matter how much instruction they receive.