This quote from the post was pulled and is now being criticized without the most important context of the article.
Sam isn't giving general career advice here -- read this advice as if you're giving it to a risk-seeking, ambitious, 19-year old (the title of the article...).
In that context -- his advice makes perfect sense.
The article isn't explicitly directed at "risk-seekers," but merely at ambitious people. It's incorrect to conflate the two. Ambition can just easily manifest itself as a desire to seek a large salary, climb the corporate hierarchy, and seek a nice lifestyle. As a member of the cohort at which this piece was directed, I don't know why everyone assumes that we want to expose ourselves to risk, or why everyone asserts that we ought to.
Why does everyone exhort the necessity of risking everything in an attempt to change the world? What is so bad about simply pursuing a nice life?
Founding yet another tumblr-for-cats and selling ads isn't ambitious either; you can do mundane work at startups just as easily as you can in a big corporation. You can do ambitious work at both of them, too. For kids who don't come from a wealthy family, there's something to be said for building up a minimal safety net early on by doing ambitious things in a relatively stable large firm. It's not the only way, though (obviously).
Sam isn't giving general career advice here -- read this advice as if you're giving it to a risk-seeking, ambitious, 19-year old (the title of the article...).
In that context -- his advice makes perfect sense.