The explanation of why there isn't any single ultimate truth

The problem with finding a single ultimate truth does not reside in reasoning, but in classification. The problem is that there isn't any both internally consistent and externally unambiguous (ie, with regard to reality) classification. Instead, there are only internally inconsistent (ie, paradoxically contradictory) and externally ambiguous classifications (like cladistics and Linnean systematics, respectively).

It means that we can think forever without finding any single ultimate truth. There simply isn't any to find. There thus isn't any "single true tree of life" as cladists claim, nor any "Higgs particle" as particle physicists claim. Instead, the idea that there is such a single ultimate truth is a fundamental misunderstanding of conceptualization, called (class)-realism, ie, the belief that classes are real. This idea is actually the only conceptual construction that conceptualization excludes. Every attempt to formulate such a "truth" will thus be either paradoxically contradictory or contradicted by facts.

The idea of a single ultimate truth is thus like the carrot in front of the donkey's eyes - a practical illusion.