All players can make mistakes. When they make them all the time you have to say that's a bad player (unless it's you in which case you say it's a great player). The odd mistake in an otherwise solid performance is different, happens to everyone, Messi, Ronaldo, Zak Knight. But if you are saying Chesney is no good because he made a mistake and therefore conclude that Theo is a good player - do you see how that doesn't follow?