As a rule, said Holmes, the more bizarre a thing is the less mysterious it proves to be. It is your commonplace, featureless crimes which are really puzzling, just as a commonplace face is the most difficult to identify.
Just as an octopus may have his den in some ocean cave, and come floating out a silent image of horror to attack a swimmer, so I picture such a spirit lurking in the dark of the house which he curses by his presence, and ready to float out upon all whom he can injure.
It has always seemed to me that so long as you produce your dramatic effect, accuracy of detail matters little. I have never striven for it and I have made some bad mistakes in consequence. What matter if I hold my readers?
While the individual man is an insoluble puzzle, in the aggregate he becomes a mathematical certainty. You can, for example, never foretell what any one man will be up to, but you can say with precision what an average number will be up to. Individuals vary, but percentages remain constant. So says the statistician.
The most dangerous condition for a man or a nation is when his intellectual side is more developed than his spiritual. Is that not exactly the condition of the world today?
I must apologize for calling so late," said he, "and I must further beg you to be so unconventional as to allow me to leave your house presently by scrambling over your back garden wall.
A study in scarlet, eh? Why shouldn't we use a little art jargon? There's the scarlet thread of murder running through the colourless skein of life, and our duty is to unravel it, and isolate it, and expose every inch of it.
The man might have died in a fit; but then the jewels are missing," mused the Inspector, "Ha! I have a theory. These flashes come upon me at times... What do you think of this, Holmes? Sholto was, on his own confession, with his brother last night. The brother died in a fit, on which Sholto walked off the treasure! How's that?" "On which the dead man very considerately got up and locked the door on the inside," said Holmes.
Well, well, my dear fellow, be it so. We have shared this same room for some years, and it would be amusing if we ended by sharing the same cell. (...)
It is a mistake to confound strangeness with mystery. The most commonplace crime is often the most mysterious because it presents no new or special features from which deductions may be drawn. This murder would have been infinitely more difficult to unravel had the body of the victim been simply found lying in the roadway without any of those outré and sensational accompaniments which have rendered it remarkable. These strange details, far from making the case more difficult, have really had the effect of making it less so.