I once managed a very intensive, very complex project that with every tool, illustrated an on-time schedule. But in the end, the project was severely delayed.
I understand the concept of "known unknowns", "unknown unknowns" and scope creep; but what is the community's guidance on the best way of anticipating the potential of schedule delays?
For instance, I understand the NASA Apollo project was subject to all the above (and more). How did the PMs anticipate delays that could have put them in Jeopardy of missing the Dec 1969 deadline?