Else, they should go into some other field of human endeavour. I don't think Shepherd made any conscious wrong decisions. The fact remains that if a batsman is given out when he is not, then the batting side suffers. It is a fact of life that one comes into the middle years, the powers of sight and hearing do take a bit of a beating. I wear multifocals myself.
Some people refuse to do so out of vanity.
And it is thus quite possible that Shepherd is not at his best. He is anything but unprofessional. But he is simply past his best. Everybody, including the man concerned, should make no bones about that. What beats me is why the ICC still refuses to use camera footage to adjudicate on catches that are doubtful, catches over which the umpire has a doubt.