This seems unexpectedly optimistic, to me. I'd think: best case = it's already done; worst case = it's impossible, but we don't know that until we've spent too

This seems unexpectedly optimistic, to me. I'd think: best case = it's already done; worst case = it's impossible, but we don't know that until we've spent too much time and money on it; the "certain obstacles" are almost always uncertain or completely unknown; and the "O time to figure out [how much time it will take] is also unknowable until the "figuring" is already complete. Now, if this were manufacturing with well-known processes, then I feel I could use your formula.