OK, the title is a bit of an overstatement, but not by much.
Brains, work ethic, and education are important, but they are never enough. People skills are the grease that enables talents to be productively employed. Leading, managing, and being a good team member all depend on people skills.
In fact, after meeting thousands of executives I’m convinced great people skills are the most important factor in career advancement. Executives who have great people skills advance farther and faster, and have better performance, than their peers.
In contrast, poor people skills is the number one reason careers falter. After all, business is not rocket science. It's rare to find someone whose career stalls because she doesn't have enough raw intelligence or adequate education. But it's common to find people who hit a ceiling because they cannot work well with others.
I firmly believe people skills can be taught and learned. Perhaps our educational institutions, as well as employers, should focus more on teaching the soft skills that are so critical to success.