What did you learn in 2012 that you will carry forth with you into 2013?
"This year, we officially crossed over from tiny to medium sized company. After running Tumblr as a team of three for nearly two years, we made it up to 50 during 2011, and will end 2012 with more than 130 wonderful men and women.
"While it's been an extraordinary privilege to come to work with so many positive and talented people, the rapid growth has presented new challenges in maintaining our culture and sensibilities.
"The biggest lesson has been the importance of constantly repeating the mission. It means spending meaningful time with everyone that joins, even if that's in a group setting. It means bringing the team together every week to talk about all of our projects, progress, and vision.
"Most importantly: It means focus, to keep everybody moving in the same direction.
"At the end of the day, we're doing more than we ever have -- and getting better every day. There's no going back now!"
More Lessons for 2013 from some of today's most innovative business thought leaders here.