The bias is that we don't even notice things that occured once. How important is there that we have a moon? That we have a continent that spans east-west? That the K-T impact happened exactly when it did?
There could be a hundred other crucial factors which we never even noticed because nobody thought they were important to the development of civilization.
East-west continent span seems irrelevant, at least for modern civilization, as it was on its way all the way from Upper Paleolithic up to something reasonably civilized in Central America too, independently, up to the point when we broke their isolation.
We have a sample of one modern human civilization, but there are some hints on how likely it was to happen.
Major types of hints are:
Data for:
Data against:
To me it looks like life, animals with nervous systems, Upper Paleolithic-style Homo, language, and behavioral modernity were all extremely unlikely events (notice how far ago they are - vaguely ~3.5bln, ~600mln, ~3mln, ~200k or ~600k, ~50k years ago) - except perhaps language and behavioral modernity might have been linked with each other, if language was relatively late (Homo sapiens only) and behavioral modernity more gradual (and its apparent suddenness is an artifact). Once we have behavioral modernity, modern civilization seems almost inevitable. Your interpretation might vary of course, but at least now you have a lot of data to argue for your position, in convenient format.