There's a large body of research that suggests that regardless of our reasons for working long hours, overwork does not help us. For starters, it doesn't seem to result in more output. In a study of consultants by Erin Reid, a professor at Boston University's Questrom School of Business, managers could not tell the difference between employees who actually worked 80 hours a week and those who just pretended to. While managers did penalize employees who were transparent about working less, Reid was not able to find any evidence that those employees actually accomplished less, or any sign that the overworking employees accomplished more.
Considerable evidence shows that overwork is not just neutral — it hurts us and the companies we work for. Numerous studies by Marianna Virtanen of the Finnish Institute of Occupational Health and her colleagues (as well as other studies) have found that overwork and the resulting stress can lead to all sorts of health problems, including impaired sleep, depression, heavy drinking, diabetes, impaired memory, and heart disease. Of course, those are bad on their own. But they're also terrible for a company's bottom line, showing up as absenteeism, turnover, and rising health insurance costs. Even the Scroogiest of employers, who cared nothing for his employees' well-being, should find strong evidence here that there are real, balance-sheet costs incurred when employees log crazy hours.
If your job relies on interpersonal communication, making judgment calls, reading other people's faces, or managing your own emotional reactions — pretty much all things that the modern office requires — I have more bad news. Researchers have found that overwork (and its accompanying stress and exhaustion) can make all of these things more difficult.
Even if you enjoy your job and work long hours voluntarily, you're simply more likely to make mistakes when you're tired — and most of us tire more easily than we think we do. Only 1-3% of the population can sleep five or six hours a night without suffering some performance drop-off. Moreover, for every 100 people who think they're a member of this sleepless elite, only five actually are. The research on the performance-destroying effects of sleeplessness alone should make everyone see the folly of the all-nighter.
Work too hard and you also lose sight of the bigger picture. Research has suggested that as we burn out, we have a greater tendency to get lost in the weeds.
In sum, the story of overwork is literally a story of diminishing returns: keep overworking, and you'll progressively work more stupidly on tasks that are increasingly meaningless.
This is something business first learned a long time ago. In the 19th century, when organized labor first compelled factory owners to limit workdays to 10 (and then eight) hours, management was surprised to discover that output actually increased – and that expensive mistakes and accidents decreased. This is an experiment that Harvard Business School's Leslie Perlow and Jessica Porter repeated over a century later with knowledge workers. It still held true. Predictable, required time off (like nights and weekends) actually made teams of consultants more productive.
Now, this is not to say we can never pull a long day. We just can't do it routinely. Most of the research I've seen suggests that people can put in a week or two of 60 hours to resolve a true crisis. But that's different from chronic overwork.
So why do we keep doing it? Why can't we put the book down?
It could be ignorance. Maybe most people just don't know how bad overwork is, objectively speaking.