Ontologies tend to ossify and become brittle, so an example that doesn't fit into one will shatter it down the line.

Ontologies are structures. Like all structures, they get brittle.

"Oh hmm, this example fundamentally doesn't fit without blowing up the whole structure."

Like in bin-packing, you want the most different examples to come at the beginning (First Fit Decreasing as a nearly optimal solution for bin-packing).

If late in the game after the ontology has ossified you receive variance you haven't absorbed in your earlier more flexible phase, it will be explosive.