"Q: What's the one thing in common among every business plan that has ever been pitched to an investor? 

A: The plan is wrong.

 Don't worry about the plan being wrong.  The plan represents a set of assumptions that hang together to produce a business venture that, if everything went according to plan, will generate positive returns for the investors and other stakeholders.  It's impossible to get all of the assumptions right.  It's management's job to adjust the plan as the assumptions don't line up.  Somethings go better than you expect.  Other things go worse.  And, there will be factors which emerge that you never considered.  That's what makes being an entrepreneur fun (and stressful!)."