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The jury is out on what should be considered “progressive” when it comes to vacation policies. IBM introduced the idea of unlimited paid time off in the 1990s—with newer tech giants like Netflix and LinkedIn also championing the movement. Proponents argue that bottomless holidays are a sign that management trusts workers to take time off when they need it. But critics aren’t so sure.

Some employees believe unlimited vacation creates a sense of guilt any time they want to take it. And early research shows that employees with unlimited vacation actually take fewer days off on average than their limited vacation counterparts.

Figuring out a vacation policy be particularly hard when you have employees around the world. Spain, for example, has 14 mandated national paid holidays for workers, whereas the US has zero, though most employers give about 10 a year, according to the US Bureau of Labor Statistics.

Amir Salihefendić, founder of the productivity startup Doist, was considering all of this when he decided to rethink his company’s vacation policy.

Doist has 60 employees in 26 countries. The complexity of building a system that would both reflect the changing nature of work and be fair to people regardless of their location (or other factors like religious traditions) convinced him that he needed to approach the idea using first principles, a problem-solving method popular with the tech crowd these days.

To reason from first principles is to break down a complicated problem into its basic elements. It’s like in math class when you reduce a fraction to its lowest terms before attempting any arithmetic. Instead of asking how might we improve this thing, a first-principles approach asks how might we design this thing if we rebuilt it from scratch.

Salihefendić didn’t want to just update Doist’s existing vacation policy, he wanted to rethink why vacation policies exist. The company’s most popular product, Todoist, is a task-management app which claims to help people “organize life, so they can enjoy it.” Salihefendić wanted the company’s policy to reflect this purpose.

“Productivity and taking time off are yin and yang,” he says. “The ability to disengage, relax, and recharge is as important as being ambitious, organized, and productive.”

Instead of trying to shoehorn everyone into a policy or a paid-holiday calendar that would be culturally relevant in 26 countries and fair to everyone regardless of religious or family obligations, Doist is doing away with company holidays. As of January 2019, Doist employees will be given 40 days off a year to use as they see fit. The only rule is that the vacation time is mandatory.

“Some of the companies building the most innovative technologies in the world are still using principles of work that are hundreds of years old,” Salihefendić tells Quartz At Work. “I hope policies like ours can inspire others to think about what it truly means to create a productive place to work.”