It’s NWBO where everything takes longer than expected and if you build in an expectation for it to take longer then they will exceed even that expectation.
Others may say, "It’s something that's never been done before, where everything takes longer than expected as it's never been done before, and if you build in an expectation for it to take longer then you risk that the time needed will exceed even that expectation, because we're discussing groundbreaking things that have actually never been done before."
There is a more dour way of saying the same thing, I guess, but not sure why one would pursue that option.