Andrew Chen, long one of the best startup/growth voices out there, just tweeted about “The Traction Treadmill” —“It’ll kill your company,” he writes. Before I go on, let me explain what he means by that term. You’ve got a startup with okay customer retention, but not great. You successfully boost growth by doubling or tripling sales & marketing spend. You’re still churning users but at small numbers, you stay ahead of this and continue to grow. It’s only once you expand into...