|Observation is not simply seeing|
The foundation of detection - and scientific method in general - is observation. Except for a few unfortunates, we all see. However, only a few of us observe. I made a concrete example of this distinction, when I demonstrated that Watson had seen the steps leading from the hall to the rooms we shared at 221 B Baker Street hundreds of times but had not observed that there were 17 of them [SCAN]. He saw, but he did not observe. In reporting another case, Watson admits:
I had heard what he had heard, I had seen what he had seen, and yet from his words it was evident that he saw clearly not only what had happened, but what was about to happen, while to me the whole business was still confused and grotesque [REDH].Watson expressed some surprise that I knew Miss Mary Sutherland was a short-sighted typist. This was visible to me but invisible to him.
Not invisible, but unnoticed, Watson. You did not know where to look, and so you missed all that was important [IDEN].While Watson was seeing her clothes (and gave me a description of them which could have graced a fashion magazine), I was observing the indentations on her wrists and on the sides of her nose.
When Inspector Gregory expressed surprise that I found a matchstick in the mud which he had overlooked, I replied: I only saw it because I was looking for it [SILV] and again when Inspector Martin expressed surprise that I noticed a bullet hole, I could only answer that I noticed it because I looked for it [DANC], You are more likely to find something when you are looking for it. The scientist is, after all, a seeker rather than a finder. It is an active process. There is nothing to be learned by staring [STUD].