In addition to steps that are hard in the sense that they can take a long time, there may also be tricky steps -- ones that have a finite window of opportunity before being precluded by some other version of events. I don't have a good enough theory of the development of civilization to defend any candidates in history, but here's a paleontological candidate:
Consider that animal lineages readily lose limbs but, once lost, almost never regain them (many-legged arthropods to six-legged insects, four-legged reptiles to two-legged birds and no-legged snakes, but no reverse transitions; the reasons for this are easy to understand in terms of the requirement of evolution that intermediate forms be advantageous). It is also clear that animals can get by well enough with two legs, but sparing two of four for toolmaking has always been a problem, let alone sparing two of two. Finally, it is clear that four legs over two is not necessarily enough advantage to displace an entrenched competitor.
The four-legged lungfish that became the ancestor of amphibians could not of course have known its distant descendents would need two spare limbs for toolmaking. If it had been delayed until a two-legged lungfish had taken the niche... it is not certain that the ultimate development of civilization would have been rendered impossible, but it is at least plausible.
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.