Sherlock Holmes wouldn’t say he never made mistakes—but would argue that they were rare indeed. It gave John the greatest satisfaction to catch him in an error—to observe what the great mind somehow missed. The fact that Sherlock’s oversights were so rare only made it sweeter on those rare occasions when they occurred.
John Watson would be the first to admit that he made mistakes. It was part of being human. Unfortunately, living with a mind like Sherlock’s did little for self esteem. It was lucky that he wasn’t inclined to have a low opinion of himself. After a bit, he stopped hearing Sherlock’s “stupids” and “idiots.” It was like living with a noisy appliance—at first, it drives you crazy, but soon it fades into the background.
But no one would ever convince them that their friendship was a mistake, no matter how little sense it made to outside observation.