To assume, however, that the observational part of philosophy, because it is not particularly laborious, is therefore easy, is a dreadful mistake, into which the student is very apt to fall, and which gives the death-blow to any possibility of his success in this study. It is, on the contrary, extremely difficult to bring our attention to elements of experience which are continually present. For we have nothing in experience with which to contrast them; and without contrast, they cannot excite our attention. We can only contrast them with imaginary states of things; but even what we imagine is but a crazy-quilt of bits snipped off from actual experiences. The result is that roundabout devices have to be resorted to, in order to enable us to perceive what stares us in the face with a glare that, once noticed, becomes almost oppressive with its insistency. This circumstance alone would be sufficient to render philosophical observation difficult — much more difficult, for example, than the kind of observation which the painter has to exercise.
C. S. Peirce (CP 1.133-4). Peirce develops the analogy to the artist's eye elsewhere; the philosopher's eye, so to speak, he takes to be a capacity of observation in a way that takes into account, and compensates for, distortions of bias, recognizing all the various ways in which one could understand whatever it is that is before the mind. See Charles S. Peirce's Phaneroscopy and Phenomenology. (ht)