He writes about how career happiness and "passion" is something that is developed over many years -- decades. Here's a favorite excerpt:
The early stages of a fantastic career might not feel fantastic at all, a reality that clashes with the fantasy world implied by the advice to "follow your passion" — an alternate universe where there's a perfect job waiting for you, one that you'll love right away once you discover it. It shouldn't be surprising that members of Generation Y demand a lot from their working life right away and are frequently disappointed about what they experience instead.
The good news is that this explanation yields a clear solution: we need a more nuanced conversation surrounding the quest for a compelling career. We currently lack, for example, a good phrase for describing those tough first years on a job where you grind away at building up skills while being shoveled less-than-inspiring entry-level work. This tough skill-building phase can provide the foundation for a wonderful career, but in this common scenario the "follow your passion" dogma would tell you that this work is not immediately enjoyable and therefore is not your passion. We need a deeper way to discuss the value of this early period in a long working life.
Read more in Cal Newport's HBR post.