Reflection begins with a collision between a system or order already in the mind, and some fragment that ought to be included in that system but remains outside of it.
A detective reflects on someone's death because there's a conflict between the fact that someone died and something already in the mind. Detectives order their experience by assuming that events have causes. This event challenges inclusion in that order. The detective makes it fit by first learning the details of the problem by reflecting and observing.
Observation is guided by what experience has taught about which details are relevant. Consequently, the detective pays more attention to bruises apparently made by some blunt instrument. The details are not obtained by focusing on a single point. The basis of a new thought must be broad. If the question was merely who might have used the blunt instrument, their would be an indefinitely large number of answers. The question is who must have done this in view of unemptied pockets, signs of a struggle, the butler's loyalty, and perhaps a hundred other things---all relevant details. A successful conclusion from a single factor alone would be an accident. The conclusion comes from all of them taken together.
The problem is to fit a detached fact into a complete surrounding system that is already assumed to be ultimate and decisive.