“First day back after paternity leave. What should I wear?” Email Comments After two months on paternity leave, Facebook CEO and new dad Mark Zuckerberg was confronted with the same dilemma all new parents face: “First day back after paternity leave. What should I wear?” His joke, posted yesterday morning, went viral within minutes, and at the time of writing has over 1 million likes.

Zuckerberg and his wife Priscilla Chan welcomed their daughter Max into the world last December, and to celebrate, pledged to give away 99% of their fortune in the form of $45 billion in Facebook shares.

But the billionaire’s joke about his clothing conundrum, posted alongside a picture showing a closet with nothing but identical gray shirts and hoodies, has a serious underlying message.

The entrepreneur wears the same outfit every day to avoid making outfit decisions he calls a “frivolous” waste of his time.“I really want to clear my life to make it so that I have to make as few decisions as possible about anything except how best to serve this community,” he told a summit in 2014.

His decision is based on a psychological theory that “even making small decisions around what you wear, or what you eat for breakfast, or things like that, they kind of make you tired and consume your energy.” According to the New York Times, he added: “I’m in this really lucky position, where I get to wake up every day and help serve more than a billion people.” “And I feel like I’m not doing my job if I spend any of my energy on things that are silly or frivolous about my life, and that way, I can dedicate all my energy to building the best products and services and helping us reach our goal and achieve our mission.”