That Startup Guy

It's been mentioned to me by some who prescribe to a school of thought that says that in creating a startup, all outcomes are knowable, and all influencing factors can be prepared for & protected against in advance. But if that's true, why do a high percentage of well- founded-funded & -advised startups still fail? I believe it comes down to 2 key elements; the human factor, and the unknowable, unlikely or improbable event. Of course, you could surely prepare against any or all of those, but in an environment of scarce resources (eg time, money, skills, expertise), I believe there to be a finite limit as to how much time can be spent 'de-risking' a project, versus actually doing the project.