The real metric of success isn't the size of your bank account. It's the number of lives in whom you might be able to make a positive difference.

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.