We work, live and operate in a complex environment and I think if we start viewing the organisation its projects and the environment in which it operates more from a systems perspective we may realise that in fact, it is truly difficult to make accurate predictions given the non-linear behaviour the system exhibits that results from all the information flows (or lack thereof), interaction of parts and other dynamics such as markets, human energy levels/mood, etc.

I really learned a lot from the book called Thinking in Systems and nowadays I can't help to look at projects, from within the context in which it operates. Definitely recommend the book for somebody wanting a bit of an introduction to that mental model.