mustard is the fool's condiment

Holmes is a very repressed, withdrawn, dysfunctional man, who has deliberately removed himself from the mainstream of his society. Particularly in the earlier stories which are firmly Victorian, Holmes is at pains to place himself outside the very rigid hierarchy of Victorian life. Holmes can’t function as a normal member of society, he doesn’t have any small talk, he doesn’t have any social life, he doesn’t have any friends. Watson is in many ways the exact opposite of that. Watson is the ultimate Victorian everyday respectable gentleman. But what brings them together and what keeps them together is that Watson would love to be Holmes, and Holmes needs to be Watson. Together they make a whole functioning individual. Without Watson, Holmes would probably kill himself, deliberately or otherwise. And without Holmes, Watson would probably die of boredom.