Full Idea
The relation of sameness remains puzzling to a psychological logician. They cannot say 'A is the same as B', because that requires distinguishing A from B, so that these would have to be different presentations.
Gist of Idea
Identity baffles psychologists, since A and B must be presented differently to identify them
Source
Gottlob Frege (Review of Husserl's 'Phil of Arithmetic' [1894], p.327)
Book Reference
-: 'Mind July 1972' [-], p.327
A Reaction
This is why Frege needed the concept of reference, so that identity could be outside the mind (as in Hesperus = Phosophorus). Think about an electron; now think about a different electron.