The best team to help your startup achieve big goals isn’t always the smartest, most talented, or best educated. Employees and leaders who find success in business have one key trait in common: they never give up.

That perseverance is what psychologists call grit -- the ability to continue working toward a goal no matter how hard it gets or how long it takes. "It is sheer determination to succeed," says Michael Matthews, a professor of engineering psychology for the U.S. Military Academy and an expert on grit. You can test yourself by taking the ‘Grit Survey’ from University of Pennsylvania.

"Excellence in life requires a lot more than a high IQ," Matthews says. People with a lot of grit pick one goal and do whatever it takes to get there. They don't give up or change course along the way, and they try creative new strategies when one tactic doesn't work. "They complete [the goal] no matter what it takes," Matthews says. Often, that means long, frustrating hours trying to learn and master new skills.

To build a successful business, it's essential to build a team that will stick with you when times get rough. Here are three tips to help you create a team that will do whatever it takes to get the job done:

1. Look for a history of perseverance. The best candidates for a growing startup will be those with serious grit, which you can assess by asking for examples of perseverance in the past. "The best predictor of future behavior is past behavior," Matthews says.

During interviews, ask candidates to share two or three stories about specific times when they took on huge, difficult challenges and stuck out the hard times to find success. Someone with multiple, substantive examples will be more likely to stick with your company through tough times.

Related: 5 Ways to Train Yourself to Be a Great Leader

2. Emphasize hard work and determination. If you emphasize innate talent or quick wins, you'll build a culture with little stamina for difficult, long-term goals. Instead, make hard work and determination part of your company's core values, and help your employees embody them.

"Engineer situations that require gritty behavior for success," Matthews says. You might offer opportunities to learn and master new skills, such as programming classes for non-programmers at a tech company, or you might set an audacious stretch goal and encourage your employees to reach for it. The employees that really embrace the challenge will be the ones to call on when you face difficult situations.

3. Reward grit when you see it. Your strongest employees may not accumulate fast or flashy accomplishments, so their value can easily go unrewarded. Think of The Tortoise and the Hare -- the tortoise has more grit and eventually wins the race, but the hare would get early accolades.

To reward that kind of determination, look for people who are quietly toiling away, improving their skills through hard work or completing difficult projects that are more arduous than enjoyable. You might call them out publicly to show others that you value their behavior, or you might just tell them that you notice and appreciate their work.

Related: 3 Ingredients for Building Effective Teams