The obstacle to reach a rational truth resides in that that “difference” is more fundamental than “similarity” is. All things are fundamentally different, not fundamentally similar. “Similarity” instead rests on “difference”, whereas “difference” is real.
The problem with this relationship is that “difference” and “similarity” can’t be consistently combined in a single statement, because such a statement has to combine the abstract with the real (like apples with a single real apple).
Inconsistently combining them in a single statement (like cladistics’ “tree of life” and particle physics’ “Higgs particle”) instead expresses a paradox, called Russell’s paradox, which thus is the connection (ie, the interface) between abstract and the real.
It all goes around and around…