Efficiency is highly overrated; Goofing off is highly underrated. Regularly scheduled sabbaths, sabbaticals, vacations, breaks, aimless walks and time off are essential for top performance of any kind. The best work ethic requires a good rest ethic.
On motivation: "I strongly believe that missionaries make better products. They care more. For a missionary, it's not just about the business. There has to be a business, and the business has to make sense, but that's not why you do it. You do it because you have something meaningful that motivates you."