One the contrary, Watson, you can see everything. You fail, however, to reason from what you see. You are too timid in drawing your inferences. Singularity is almost invariably a clue. The more and featureless and commonplace a crime is, the more difficult it is to bring it home.
Circumstantial evidence is a very tricky thing.
It may seem to point very straight to one thing, but if you shift your own point of view a little, you may find it pointing in an equally uncompromising manner to something entirely different. There is nothing more deceptive than an obvious fact. I should prefer that you do not mention my name at all in connection with the case, as I choose to be only associated with those crimes which present some difficulty in their solution. We approached the case, you remember, with an absolutely blank mind, which is always an advantage. We had formed no theories.