At the gym, you won't grow stronger unless you experience a little pain. The same is true in life, according to both science and the super successful. 

One Yale study showed your brain's learning center lights up when you're confronted with stressful unpredictability and goes dark when your situation is stable and comfortable. Or, as one five-time entrepreneur puts it, those looking to maximize their success "should strive to have at least 70 percent of their time doing things that are really difficult" as "these are the tasks that result in the most growth."

But while it's a fact that doing uncomfortable, scary things maximizes personal growth, it's equally true that it can be terrifying. How do you push yourself to take enough risks without making your life thoroughly unpleasant or stumbling into a situation you really can't handle? On Quartz recently, Bank of the West CEO Nandita Bakhshi offered a surprisingly simple (but powerful) answer. She calls it the rule of thirds.

One third "pure white-knuckle terror" is good for you. 

As a woman and an immigrant, Bakhshi experienced a lot of external doubt on her climb to the top of her industry. That led her to battle plenty of internal doubts, too. Was she capable enough for the next step up in her career journey, she often asked herself. 

Bakhshi noticed that her male colleagues, by and large, weren't troubled by this kind of self-doubt as she was. They would hurl themselves headlong into jobs and projects they were only minimally qualified for, confident they'd learn on the fly. Bakhshi realized she'd need similar self-belief to rise, so she set herself a simple rule. 

"It was all right, I would tell myself, to take on a position that was 'one third in my comfort zone, one third a stretch, and one third pure white-knuckle terror,'" she explains. "It was my prosaic and pragmatic adaptation of Robert Browning's celebrated insight, 'Ah, but a man's reach should exceed his grasp. Or what's a heaven for?'"

This simple formula isn't a guarantee of success or a cure-all for imposter syndrome, Bakhshi acknowledges, but she insists "the rule of thirds has worked for me." 

And you need not be a member of an underrepresented group to utilize it. Every one of us sometimes has moments of doubt before we embark on a challenge. The rule of thirds is a simple reminder that such feelings aren't just normal, but actively positive. If you're not terrified a third of the time, you're probably not pushing yourself hard enough to reach your full potential. 

Or as Bakhshi reminds challenge-shy readers closing her article: "You don't have to be an instant expert in a more senior role you've never held before. You just have to be willing to follow the rule of thirds."