Both this "90-90" and "80-20" indicate that the devil is in the detail. e.g. You can expect surprises as you're almost done, there's an inherent complexity to t

Both this "90-90" and "80-20" indicate that the devil is in the detail. e.g. You can expect surprises as you're almost done, there's an inherent complexity to the solution, etc. But saying "the first 90% takes 90% of the time" blatantly ignores these anticipatable unknowns; so it's a much more tongue-in-cheek thing to say.