Call it the paradox of entrepreneurship: The very thing it takes to start a business often ends up destroying it.

I've spent the past 15 years researching people who start companies, and there's a consistent theme among the 16,000 founders I've analyzed. It's passion. Founders believe in their ideas so strongly they throw aside comfortable jobs and risk their life savings to chase their dreams. They have such contagious enthusiasm they can convince others to sign on, whether it's co-founders or venture investors or early-adopting...