Top performers are often categorized as those who accomplish the most. People who knock out long task lists every day are at the top of their game, right?

According to Morten Hansen, a professor at University of California, Berkeley and author of Great at Work, we've been looking at it all wrong. Rather than focusing on 'work smarter, not harder,' we should be mastering a new and improved practice: "do less, then obsess."

Hansen found this is the most important of the seven key work practices discovered in his study of more than 5,000 managers and employees in corporate America. Top performers living by the motto took on a tiny set of priorities, then went all in to excel in those few areas.

Those who 'do more,' Hansen says, fall into two performance-hindering traps.

"First, they spread themselves too thin and thus wind up excelling at nothing. Second, they encounter complexities and coordination costs as they try to juggle all those activities," he said.

However, those who "do less, then obsess" hold an advantage over others because they can deliver exceptional work.

"You can only obsess to excel if you pursue a few things at the time," Hansen continued. "But if you do, the quality of your output will set you apart."

Obsessing to excel in your own career won't look like everyone else's. Each process depends on your line of work and the end goal you're hoping to achieve.

Here's why you need to drop the old 'work smarter, not harder' cliche and start obsessing about work:

1. Multitasking is overrated and painful.

Success and adrenaline go hand-in-hand. Fighting for our career goals and dreams causes many people to multitask their way to the finish line.

Unfortunately, like many of us, James Murphy, VP of sales at SiteLock, a global website security firm in Scottsdale, Arizona, found multitasking wasn't the answer.

"I reached a point where I had spread myself so thin, I was unable to affect change. Being a leader, I needed to deliver results but also commit time to my team," Murphy explained. "Unfortunately, the leadership part fell to the side and I wound up falling flat on my face."

This type of burnout is all too common. It leaves many employees -- not just leaders -- overwhelmed and falling short of their potential.

Luckily, Murphy had the opportunity to turn his career around when a mentor saw him struggling.

"He told me that the quantity of tasks you produce is unimportant -- it's the impact those tasks have on the business that matters," he continued.

Give employees a few responsibilities and voice your expectations immediately. Their ability to excel in a few aspects of work will grow as you encourage each small success.

2. Half-assing two things gets you nowhere.

Ashley Davidson, senior director of media and industry relations at Fish Consulting, a PR firm headquartered in Ft. Lauderdale, Florida, recently shared one of her favorite quotes with me: "Never half-ass two things. Whole-ass one thing."

This famous quote from Nick Offerman's character in TV show "Parks and Recreation" speaks to every company leader -- no matter their industry.

"We're all over-worked, over-scheduled, and pulled in a dozen different directions on any given day," Davidson said. "I've seen it across our agency. When people are given the opportunity to hone in on what's really important and what they excel at, they'll deliver the best results."

Employees shouldn't waste talent and energy on mundane tasks they don't care about. Instead, help your team find the one thing they'd like to "whole-ass." Discuss their current roles, what they're passionate about, and areas where you've noticed their natural strengths shine.

Take time to recognize their obsessions and create a plan to make it their main focus. You'll find employees can deliver better results and are happier in their roles.

3. Multiple options create indecision.

Employees who are torn between various responsibilities are unsure what to focus on. This leads them to focus on everything.

Geoffrey Woo, CEO of HVMN, a biometrics company located in San Francisco, saw the detrimental effects of multiple options and responsibilities when they overtook his head of engineering, Paul.

"Our company couldn't be as strategic and deliberate as we wanted because our engineering team was always just able to react," Woo said.

After being given the opportunity to focus all of his efforts on customers, Paul is now at the top of his game. HVMN is feeling these effects with the lifetime value of customers and initial conversion rates doubled.

Find out how you can keep unnecessary options and responsibilities away from employees. Then, create clearly defined roles and let them dive into their passions.