He didn't invest in the company. He was granted shares. He sold them at his first chance.
Thing is Jason is all about living the good life not being rich. Good life != rich. He was doing well for himself before Basecamp and Basecamp was just part of his strategy to manage his own work more effectively so he would have time for stuff that is actually better than coding or designing - like spending time with family or driving race cars a la DHH.
Thing is Jason is all about living the good life not being rich. Good life != rich. He was doing well for himself before Basecamp and Basecamp was just part of his strategy to manage his own work more effectively so he would have time for stuff that is actually better than coding or designing - like spending time with family or driving race cars a la DHH.