Nearly 40 percent of employees are so burned out they want to quit—and work-life balance isn't to blame

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Your best employee might be ready to quit. A recent survey taken this fall found that nearly 40 percent of the 2,000 U.S. adult workers surveyed were thinking of leaving their jobs thanks to burnout.

That's a chilling statistic for any manager, especially in a tight labor market. But the survey, conducted by HR consulting firm Randstad US, revealed another surprising fact: work-life balance wasn't the key reason employees felt burned out. Instead, workers cited stalled careers and managers that didn't seem to appreciate them.

CNBC Make It talked to Jim Link, chief human resources officer at Randstad North America. He took us through the top reasons surveyed workers feel burned out and what they and their bosses can do about it.

1. Lack of career growth

A stalled career was the No. 1 driver for burnout among employees surveyed. According to Link, you're more likely to feel this way if you work in a deadline-driven environment with constrained resources.

A "task-oriented" work environment can make workers feel they are running on a hamster wheel, says Link. In order to deliver results, employees often minimize outside distractions, including longer-term career objectives. "It's all a very big cycle...and it's the role of both the employee and the employer to break that cycle," explains Link.

What employees can do: Remember that your boss isn't a mind reader. Schedule time to have a frank discussion about what your career progression might look like. You can also tap into your peer network of trusted colleagues to get feedback on what you're doing well and what you need to improve on to ready yourself for that next job or promotion.

What managers can do: Ask employees about what's truly important to them and what they hope to achieve long term. You can also provide career development and learning opportunities for your team. Acquiring new skills can keep employees from feeling stagnant and boost their overall satisfaction level.

More importantly, help staffers understand how even the most mundane tasks are tied to the company's success. "Most folks get caught in the day-to-day cycle and they forget that there's a connectivity between what they're doing and the goals of the company," says Link.

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2. Lack of appreciation

It's natural to want your efforts valued. That's why more than 40 percent of surveyed employees said their burnout was caused by a boss who didn't appreciate their work.

What employees can do: Ask your boss to discuss positive aspects about your work performance. Just asking the question can give you the positive feedback that can get lost in the hustle and bustle of the work day. Next, ask what you need to do differently. Supervisors love when employees ask for areas of improvement because it shows an openness and a willingness to learn, says Link. By asking how you can improve, you'll also discover a new way to feel challenged and engaged.

What managers can do: Understand that young employees really crave feedback, especially when it's constructive, says Link. Set up times to review your employees' job performance so they have a firm grasp on what they're doing well and areas that need work. Also, remember to offer up kudos or dole out praise when employees meet and exceed expectations.

3. Overloaded schedules

The pressure to get more done than is possible within the work day was also a top driver of burnout, according to the survey. While overloaded employees may be able to deliver for some time, says Link, their job satisfaction and work performance will eventually decline.

What employees can do: Make it clear to your manager that your workload is not realistic. Link recommends this three-step process to help you navigate the conversation. He says to explain: Here's what I'm tasked with doing, here are the number of hours it takes to finish each task and here are the priorities I need clarified or changed.

What managers can do: Give your employees time to decompress and realize that there isn't a one-size-fits-all solution to burnout, says Link. What one person can easily handle, another might find overwhelming. Work with your employees to find remedies that are as unique as they are and tailor their workload based on what they can handle — and within reason.

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