The only way to avoid burnout as an entrepreneur is to viscerally believe that the work you’re doing is going to impact a part of the world you genuinely care about. Many people believe that when a great financial business opportunity presents itself, it’s crazy not to take the risk and go for it. However, I firmly believe that “an incredible business opportunity” is not enough to make you the person for the job, instead the real question is: do you have a burning passion for the product you’re building and the customer you’re serving? Arriving at this understanding wasn’t easy. In fact, it took the better part of my career to grasp.

I launched my first startup when I was an undergrad studying computer science. The idea was simple: hire notetakers for the most popular university classes, and help them post their notes online for other students to access for free. In less than two years, we were able to raise venture capital, scale the company to over 200 universities and 10,000 courses around the country, before eventually selling the company. Soon after, I became the founding CTO of Stubhub.com, an online ticket reseller. As someone who didn’t go to a lot of concerts or sporting events, it was my first time building something for an audience I wasn’t familiar with. While I initially didn’t recognize this as a problem, I soon came to understand that as an entrepreneur, a deep connection with your mission trumps everything else. Without it, it’s extremely hard to motivate yourself through the ups and downs of an early stage company. Despite a great market opportunity and a product that many people loved, I decided to move on before seeing it through to the end.

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At this point I had two startups under my belt when an investor, a friend, and myself came up with the idea for a brick and mortar “category killer” store for extreme athletes — REI but for X Games sports. My experience building ecommerce platforms coupled with another great market opportunity piqued my interest. Frankly, I had an inkling that this might not be my passion, but I dove in anyway. Skateboarders and surfers couldn’t get enough of us and I got to build some really cool retail systems and in-store experiential technology. However, to say I am not an extreme athlete is an understatement. It wasn’t long before I realized I had done it again: I had founded another company where I could not relate to our customers and didn’t viscerally care about the product I was building.

My next career move landed me at Amazon (AMZN). If I wanted to build a big successful company one day, I had to understand how a well-run company actually worked. Amazon Web Services was the first opportunity I had to work on a platform that was built for developers. As a developer myself, I understood who we were building for, their needs, and their challenges. It was here that I finally regained the conviction I hadn’t had since my first company; it was empowering.

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So when I got the entrepreneurial itch again, I knew that I could not make the same mistake I had made in the past. My goal was to build something that would 1) answer a challenge I had faced at all three companies and 2) serve an audience I could relate to. I had learned early on that developers could have huge influence on their company’s’ success if you give them the right tools. I had also realized that at every company, the customer experience is critical and that experience is driven by communications — something that was expensive, clunky, and pretty archaic to implement. And so, Twilio was born, a developer platform for communications.

Twilio was not one of those ideas that everyone immediately loved — if you weren’t a developer or had never encountered the need to communicate to build a better business (as I had at all three of my companies), it may not have made much sense. But I had the deep-rooted understanding of our customer to know that if it worked, it had the potential to be disruptive. That passion carried me through the more trying times; when we struggled to find funding, and when other entrepreneurs and investors I respected told me Twilio was unlikely to succeed. But ultimately, my instinctual commitment and passion for the core concept overcame the self-doubt all early stage founders experience. My advice to early stage entrepreneurs — or anyone trying to figure out their next move — is to ask yourself early on, “What’s my connection to this company and our customers, and am I the best person to carry out its mission?” The answer needs to be a resounding yes, or else you risk losing the burning fire that ultimately gets you through the toughest times in your career.

Read all responses to the Leadership Insider question: “What’s the most important lesson you’ve learned in your career?”

The Best Way to Deliver Bad News to Employees by Jim Whitehurst, CEO of Red Hat.

You Should Never Hire A Job Candidate Without Doing This First by Phil Friedman CEO of CGS.

The One Quality A Leader Should Never Lack by David Silverman, CEO of McChrystal Group.

What This CEO Learned From a $40 Million Mistake by Brad Smith, CEO of Intuit.

The Most Valuable Lesson You Learn As An Entrepreneur by Shahrzad Rafati, founder and CEO of BroadbandTV.

Why It Pays To Be Nice at Work by Erin “Mack” McKelvey, CEO of SalientMG.

The key to a successful career change: start a blog by Peter Thomson, marketing director of SeedInvest.

The secret to dealing with difficult coworkers by Clark Valberg, CEO of InVision.

The best way to plan for a successful career? Forget the plan by Stephen Cannon, CEO of Mercedes-Benz USA.