More than 700 million days of paid time off go untapped every year by American workers. Stress in your workplace? If you can’t cut it with a knife, you can probably at least see a little of it lurking in the dark corners. It’s a fact: If your employees are doing great work–setting and meeting deadlines, inventing new ways of doing things, and generally killing it in your area of expertise–they are, on some level, suffering for it.

That’s why businesses give their employees paid time off (PTO) as one of the basic perks that come with a full-time job. But people just aren’t making use of that time off the way they should.

Why is that? I’m betting that they drink as much coffee as they’re offered in the break room. I’m sure they gladly claim their full health-insurance and retirement plan benefits and happily accept every bit of compensation in their paychecks. But why does the average American worker, who gets 23.2 days of PTO per year, only use about half of those days and let the others go to waste? I mean, according to Project: Time Off (affiliated with the U.S. Travel Association), workers drag themselves off to work on an unbelievable 705 million days when they could have been on vacation.

I’ve given this a lot of thought, because I know (and you should, too) that people who take time to spend with their spouse and kids, visit relatives, explore new places, see sights, or just chill out somewhere are better workers and happier people. Better and happier leads to a more productive, less stressed workforce. And that leads directly to success and fulfillment, both on a corporate and an individual level. So here are my top reasons why people miss out on the PTO they deserve, and how to overcome them

Fear of Missing Out (or Fear of Not Being Missed)

According to Project: Time Off, one reason people aren’t taking those days is concern that they will fall behind at work–or look too replaceable or dispensable. That’s something the company leadership has to nip in the bud. Make it crystal clear that everybody is expected to take time off, and create a culture in which they are backed up (not criticized) for that decision. This is no place for mixed messages.

Work Martyrdom

Project: Time Off points out in its report State of the American Vacation 2018 that managers should look out for an apparently dedicated employee who is really a “work martyr” in disguise. Don’t let this culture get a foothold at your place of work.

Make sure resources are allocated to training people in a collaborative, cooperative way in your business so people can back each other up. That way, the absence of one or two employees will never be enough to throw a monkey wrench into the works, and nobody will feel chained to his or her desk or snowed under by excess workloads. That’s the sign of a well-run workplace anyway.

Lower-Level Employees May Need It Most, But Take It Least

Project: Time Off found that vacation martyrdom is less of an issue with executives and senior leadership.  Some 70 percent of them believe their company wants them to use their vacation time, and 64 percent also believe it’s okay to talk about their vacation experiences when they come back to the office.

Conversely, 54 percent of employees at lower levels are unsure whether they should even mention their vacations once back on the job. The message for leadership: Create a culture in which recharging is not seen as something for a privileged class only, but something that everyone from the entry-level cubicles to the C suite gets to take advantage of.

So, What’s a Leader to Do?

The numbers don’t lie. When you create what Project: Time Off calls a “positive vacation culture,” meaning you encourage people to take time off–and they believe it’s sincere–happiness grows in several areas. Happiness with the company reaches 72 percent–that’s 30 percent better than you’ll see in a discouraging environment where people are afraid to take their vacation days.

Happiness in physical health and well-being, personal relationships, and even taking joy in the job itself, all are better in a vacation-positive workplace.

If you can’t honestly say your workplace has a positive vacation culture, it’s time for a revolution. And, like the best adventures, it all starts with a plan. Get out a note pad and start writing down ways to market it to your people. Do it now before summer vacations are upon us.