How is it possible that this number that costs billions of dollars doesn’t have a clear and universally accepted definition Because design constraints are not

How is it possible that this number that costs billions of dollars doesn’t have a clear and universally accepted definition Because design constraints are not universal across all projects. Human error for something like the space shuttle is fairly minimal considering the mind boggling amount of training that's done. If you have an unreliable or unproven materials provider then that present a design constraint that must be accounted for. Etc.