To realize how outdated the five-day, 40-hour workweek is, you have to know where it came from.

Before 1900 the average American worker worked more than 60 hours a week. A standard schedule was ten-hour days, six days a week. The only structural limits to working were lighting and religion. You stopped working when it was too dark to see or to go to church. It was exhausting. It was often fatal.

Unions helped turn this around. In 1916, railroad unions demanded an eight-hour work day, largely because work after that point correlated with a rise in accidents and death. The railroads declined. So workers went on strike. America’s rail system nearly came to a halt.

This was during World War I, when transporting military equipment by rail was vital to national security. President Woodrow Wilson, desperate to get the trains moving, asked congress to write an eight-hour railroad work day into law. He told a joint session in 1916:

I have come to you to seek your assistance in dealing with a very grave situation which has arisen out of the demand of the employees of the railroads engaged in freight train service that they be granted an eight-hour working day … I turn to you, deeming it clearly our duty as public servants to leave nothing undone that we can do to safeguard the interests of the nation.

It worked. Congress passed the Adamson Act, and overtime pay after an eight-hour day became railroad workers’ right.

Twenty years later, the New Deal pushed for broader workers’ rights. It used the Adamson Act as a template, as no one wanted to favor one field over another. The eight-hour, five-day workday was standardized for all industries.

Eighty years later this work schedule – originally designed for the endurance constraints of railroad depot workers – has become so ingrained that we rarely question it, regardless of profession.

Which is crazy.

The biggest employment change of the last century is the number of careers that shifted from physically exhausting to mentally exhausting. From doing stuff with your arms to doing stuff with your head.

Since the constraints of physically exhausting jobs are visible, we took decisive action when things weren’t working, like the Adamson Act. But the limits of mentally exhausting jobs are nuanced and less visible, so we get trapped in a spot where most of us work a schedule that doesn’t maximize our productivity, yet we do nothing about it.

Every person I’ve worked with comes back from vacation saying some variation of the same thing:

“Now that I had some time to think, I’ve realized …”

“With a few days to clear my mind, I figured out …”

“While I was away I got this great idea …”

The irony is that people can get some of their most important work done outside of work, when they’re free to think and ponder. The struggle is that we take time off maybe once a year, without realizing that time to think is a key element of many jobs, and one that a traditional work schedule doesn’t accommodate very well.

Not all jobs require creativity or critical thinking. But those that do function better with time devoted to wandering and being curious, in ways that are removed from scheduled work but actually help tackle some of your biggest work problems.

It’s just hard to do that because we’re set on the idea that a typical work day should be eight uninterrupted hours seated at your desk. Tell your boss you found a trick that will make you more creative and productive, and they ask what you’re waiting for. Tell them that your trick is taking a 90-minute walk in the middle of the day, and they say no, you need to work. Another way to put this is that a lot of workers have thought jobs without much time to think.

David Leonhardt of the New York Times recently wrote about former Secretary of State George Shultz, who carved out time to sit and wonder:

His hour of solitude was the only way he could find time to think about the strategic aspects of his job. Otherwise, he would be constantly pulled into moment-to-moment tactical issues, never able to focus on larger questions of the national interest. And the only way to do great work, in any field, is to find time to consider the larger questions.

That last sentence is crucial for anyone whose jobs involves strategy, analysis, creativity, innovation, managing people, non-structured decision-making, or really anything outside of repetitive tasks.

The “moment-to-moment tactical issues” Shultz refers to are what happens in the office during the eight-hour, five-day workweek. Meetings. Spreadsheets. Meetings. Phone calls. Meetings.

The “larger questions” often can’t be tackled at work, because creativity and critical thinking require uninterrupted focus – like going for a walk or sitting quietly on a couch by yourself. Or a bike ride. Or talking to someone outside your field.

Steve Jobs did most of his serious conversations while walking. Tim Armstrong spends four hours a week just thinking. Jeff Weiner does something similar. Jack Dorsey famously wanders about. Someone once asked Charlie Munger what Warren Buffett’s secret was. “I would say half of all the time he spends is sitting on his ass and reading. He has a lot of time to think.”

Amos Tversky, the late collaborator of Nobel-winning psychologist Daniel Kahneman, once said “the secret to doing good research is always to be a little underemployed. You waste years by not being able to waste hours.”

The same is true for a lot of jobs.

The traditional eight-hour work schedule is great if your job is repetitive, customer-facing, or physically constraining. But for the large and growing number of “knowledge jobs,” it might not be.

You might be better off taking two hours in the morning to stay at home thinking about some big problem.

Or go for a long mid-day walk to ponder why something isn’t working.

Or leaving at 3pm and spend the rest of the day envisioning a new strategy.

It’s not about working less. It’s the opposite: A lot of knowledge jobs basically never stop, and without structuring time to think and be curious you wind up less efficient during the hours that are devoted to sitting at your desk cranking out work.

There’s never going to be an Adamson Act for knowledge workers who need time to think. It’s up to you to figure it out. The first step is realizing that taking time in the middle of your day to do stuff that doesn’t look like work is the most important part of your work day.