Trust your gut instinct over spreadsheets. There are too many variables in the real world that you simply can't put into a spreadsheet. Spreadsheets spit out results from your inexact assumptions and give you a false sense of security. In most cases your heart and gut are still your best guide.
Successful entrepreneurs find the balance between listening to their inner voice and staying persistent in driving for success - because sometimes success is waiting right across from the transitional bump that's disguised as failure.
In the business world today failure is apparently not an option. We need to change this attitude toward failure - and celebrate the idea that only by falling on our collective business faces do we learn enough to succeed down the road.