Mark Zuckerberg's Unpredictable New Year's Resolutions

— -- Facebook CEO Mark Zuckerberg is known for choosing an ambitious personal challenge to take on at the start of each year.

The new father, 31, hasn't yet announced what his 2016 challenge will be. Judging by his previous resolutions, what Zuckerberg will do next is anyone's guess; however, he has an impressive track record of declaring a goal and sticking with it.

Over the course of 2015, Zuckerberg committed to reading a new book every other week and announced each title on the "A Year of Books" Facebook page.

"Reading has given me more perspective on a number of topics -- from science to religion, from poverty to prosperity, from health to energy to social justice, from political philosophy to foreign policy, and from history to futuristic fiction," Zuckerberg wrote this week on his Facebook wall. "This challenge has been intellectually fulfilling, and I come away with a greater sense of hope and optimism that our society can make greater progress in all of these areas."

His personal challenges span a broad spectrum. In 2009, Zuckerberg vowed to wear a tie every day to work (his hoodies and t-shirts have become his trademark).

The next year, he taught himself to speak Mandarin, a language that is not only important in the business world, but one spoken by many members of Zuckerberg's wife's family.

The world got to see the payoff last October when Zuckerberg charmed a crowd at Tsinghua University in Beijing by participating in a 30-minute question and answer session in Mandarin.

Zuckerberg's challenge in 2011 was to become a vegetarian and only eat meat if he butchered the animal himself.

"The reason for this is that I feel lucky for having such a great life," Zuckerberg wrote on his Facebook page. "I like eating meat and before this year I ate it almost every day. In order to practice thankfulness, I want to be more connected to the food I eat and the animals that give their lives so I can eat them."

For 2012, Zuckerberg set a goal to return to coding -- something he hasn't had a chance to do as Facebook as grown in scope.

In 2013 Zuckerberg made it a point to meet someone new outside Facebook every day.

In 2014, the tech titan wrote one thank you note per day, which he admitted was a surprisingly difficult challenge.

"There are people who see the beauty of things," he told the audience. "Then there are people who see things and want to make them better, and I tend to be the latter."