Of course, this is not to imply that it's necessarily possible to know every requirement perfectly before you begin - I find that I frequently don't really understand the requirements until I've built the damn thing and it's made first contact with the real world.
So I usually toss that first version out, and build the second one. And that one is usually good enough that I don't immediately want to throw it out the window.
And by the time I get through the third version, usually a fair bit after the second is done, it's pretty damn good.
Because now I understand the problem and the requirements so much better than I did at the start, and I better understand what the system needs to be to solve that problem.
Will it be perfect? Never, except in a static and unchanging universe. But we can approach optimality for a given moment in time, which is functionally the same thing.