"Recognising, as I do, that you are the second highest expert in Europe" "Indeed, sir! May I inquire who has the honour to be the first?" Asked Holmes, with some asperity. "To the man of precised, scientific mind the work of Monsieur Bertillon must always appeal strongly." "Then had you not better consult him?" "I said, sir, to the precisely scientific mind. But as a practical man of affairs it is acknowledged that you stand alone. I trust, sir, that I have not inadvertently--" "Just a little," said Holmes.

…but it is better to learn wisdom late than never to learn it at all.

I am not the law, but I represent justice so far as my feeble powers go.

It is more than possible; it is probable.

You're not hurt, Watson? For God's sake, say that you are not hurt!" It was worth a wound -- it was worth many wounds -- to know the depth of loyalty and love which lay behind that cold mask. The clear, hard eyes were dimmed for a moment, and the firm lips were shaking. For the one and only time I caught a glimpse of a great heart as well as of a great brain. All my years of humble but single-minded service culminated in that moment of revelation.

So swift, silent and furtive were his movements like those of a trained bloodhound picking out a scent, that I could not but think what a terrible criminal he would have made had he turned his energy and sagacity against the law instead of exerting them in its defense. -Dr. Watson, The Sign of the Four

Depend upon it there comes a time when for every addition of knowledge you forget something that you knew before. It is of the highest importance, therefore, not to have useless facts elbowing out the useful ones.