Disagree entirely. If "Every new piece of software can be broken down to pieces that are very similar to other software that had been done before", you are talk

Disagree entirely. If "Every new piece of software can be broken down to pieces that are very similar to other software that had been done before", you are talking about assembling library components, not programming (though as you say even that often comes with its own unforeseeable difficulties). This is the fundamental paradox of software development estimation (and separate to the uncertainty of external forces): when you try to estimate development you are estimating design of something that has never been made before. If you aren't, you should probably be buying a product instead of building. It's a fool's errand basically.