I walked into the interview room, and an energetic young guy (we’ll call him Chen) ran up to me and shook my hand frantically with both of his. He was interviewing for a software engineering position.

“Hi, I’m Chen!” he said brightly. “I’m so happy to meet you!”

During his interview, Chen overwhelmed me with his enthusiasm. He was open to feedback, asked clarifying questions, and stayed extremely upbeat. Staying upbeat was impressive because he could surely tell he was doing a poor job solving my design problem.

During the final five minutes, when candidates can ask questions, Chen posed as many as he could fit in (I let the interview run over). He demonstrated a knowledge of Amazon’s business and history and explained how he would put in any energy necessary to be a successful part of the company.

When we did our debrief at the end of the interview, every interviewer had the same impression. Chen was below the bar on all technical measures (design, coding, algorithms). On the other hand, he was enthusiastic, energetic, self-critical about his technical gaps, and excited to hear constructive feedback, and he demonstrated a drive to improve himself.

In leading many hundreds of Amazon interviews as both a bar-raiser and a hiring manager, I’ve seen all types of candidates. I’ve also seen all the ways that candidates miss out on an opportunity to get hired.

When candidates prepare to interview at a company like Amazon (or Facebook, Google, Apple, etc.), they almost always focus on the functional aspects of the job. Software engineering candidates spend hours refreshing their knowledge of common coding questions. Designers build a beautiful portfolio of every UX they’ve worked on.

Soft skills don’t require the same type of preparation, but they’re just as essential to the interview process. Do you care about this being your career? Do you understand the company you’re thinking about joining? Are you able to demonstrate that you’ll be a great co-worker, not just a knowledgeable one?

Employees with soft skills provide leverage to a team. They don’t just contribute their work, but also improve their coworkers’ efforts.

I’ve seen dozens of people fail at Amazon, and 80 percent do so because of soft skill issues. They fail because they’re jerks. They fail because they don’t listen to their co-workers. They fail because they can’t take feedback. They fail because they don’t handle mistakes well.

In training new bar-raisers at Amazon, we emphasize that excellent leadership principles are at least as important as—if not more important than—functional skills. While failure or success at functional skill interview questions are easier to judge, we insist that the loops look very carefully at the soft skills as measured by our leadership principles.

A functional team is more valuable than an individual with functional skills. An amazingly skilled jerk does not add nearly as much value as a team member who encourages the team and helps drive them to do the right thing.

Functional skills can be taught. Coursework, books, and experience are great at filling in knowledge gaps. It’s significantly harder to teach a person not to be offended when someone says their code needs better documentation or their project plan doesn’t cover important milestones. I haven’t seen a ton of success in teaching people empathy.

Employees with soft skills provide leverage to a team. They don’t just contribute their work; they also improve their co-workers’ efforts. They inspire colleagues to stay on the team longer, which adds to institutional knowledge, improving productivity even more. These people are aware they can always learn more and are therefore open to new ideas. Soft skills are critical for growth, and in the long run, growth potential is more important than existing functional skills.

As I’ve written about before, there are ways to demonstrate soft skills in an interview. You can show that you’ll not only be a skilled worker, but that others will enjoy working with you. You can demonstrate that you’ll not only add your functional skills to the company, but also improve the productivity and happiness of those around you.

In our debrief for Chen, we agreed that he missed the technical bar across the board. On the other hand, we also agreed that we would love to work with him. We made him an offer. He has been at Amazon for years, has been promoted a couple of times, and has repeatedly demonstrated that enthusiasm and soft skills are powerful tools for long-term success.