(Sektion 216: Philosophische Untersuchungen von Ludwig Wittgenstein).
216. "A thing is identical with itself."--There exists no better example of a useless proposition that is yet connected with a play of the Vorstellung. It is as if, in Vorstellung, we layed the thing into its own shape and saw that it fit.
We could also say: "Every thing fits into itself."--Or another: "Every thing fits into its own shape." One looks at a thing and imagines that there is a blank left for it and that it now fits exactly into itself.
Does this spot * 'fit' into its white surrounding?--But that is exactly what it would look like if there had first been a hole and it now fit into it. With the expression "it fits" we do not even describe this picture. Not even this situation.
"Every colored patch fits exactly into its surrounding" is a somewhat specialized proposition of identitiy.