David Heineimeier Hansson, the creator of Ruby on Rails and partner at 37signals in Chicago, says that planning is guessing, and for a start-up, the focus must be on today and not on tomorrow. He argues that constraints–fiscal, temporal, or otherwise–drive innovation and effective problem-solving. The most important thing, Hansson believes, is to make a dent in the universe with your company. ┬áLecture delivered at Stanford University.