So why is Watson so modest? Watson isn't just complimenting Holmes, as in, telling us how great he is. He's also complementing Holmes, or in other words, showing us Holmes's genius by providing a constant point of comparison. After all, Watson's a smart man – a medical doctor with a clear, cool writing style. He's someone we respect. And if Holmes is smart enough to make a war vet doctor feel dumb, well then, Holmes must be brilliant.