Last week, Arianna Huffington said Elon Musk’s lack of sleep is impairing his performance. “The science is clear," she wrote after Tesla’s chief executive officer told the New York Times that he works 120 hours a week, leaving him with little time to rest.

Yet science doesn’t show a clear positive relationship between sleep duration and cognitive ability. When it comes to sleep—as in much else—quality matters more than quantity.

Although Huffington published a best-selling book about sleep in 2016, the only scientific publication she cited in her open letter to Musk was a 2000 paper that likened the performance of a person awake for 17 to 19 hours to that of someone with a 0.05% blood alcohol content, which is about equal to the level for a 180-pound man after drinking two beers within an hour. It’s not a horrible condition to be in by the end of the working day and not sufficient to cause serious impairments to decision-making. The Centers for Disease Control and Prevention recommend at least seven hours of sleep, which means 17 waking hours a day, enough to produce that two-beer sluggishness.

Sleeping more doesn’t necessarily help. A recent Dutch study revealed an inverted U-shaped association between sleep duration and middle-aged men’s cognitive performance: Those who slept less than six hours or more than nine hours a day performed worse than those in between. Another recent paper showed that in young adults, shorter sleep duration was associated with higher persistence and overall better ability to plan, organize and complete tasks despite higher fatigue levels. According to this study, conducted in Japan, young people who sleep four to six hours a day are likely to be better workers than those who sleep longer.

The large body of academic work on the relationship between sleep and performance reveals that low sleep quality is more strongly correlated with different kinds of failure, depression and aggression than short sleep duration. I wouldn’t presume to know what, if anything, is wrong with Musk’s health, but judging by his candid interview with The New York Times, he has a sleep quality problem. He says he sometimes needs medication to get any downtime.

A 2016 report from the National Sleep Foundation identified a number of specific sleep quality indicators. Someone who sleeps well, for example, doesn’t spend more than 45 minutes in bed before drifting off or wake up for more than 41 minutes during the night. Healthy “sleep efficiency"—the relation of sleep time to time spent in bed—is more than 74% for adults. The duration of various phases of sleep is also important for determining quality.

Sleeping more and working less clearly doesn’t sound like a good idea to Musk. “You think this is an option," he tweeted in response to Huffington. “It is not."

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He’s not just speaking for himself: even when you’re not physically at work, it’s difficult not to think about it if you’re emotionally involved and motivated. And, of course, people are reachable around the clock these days—and if what you do gets the outside world’s attention, you’re also open to the never-ending, pitiless goading, bullying and misinformed meddling of the social networks.

All this makes it much more difficult to sleep well than to sleep longer. Making time for vacations and family doesn’t work for anyone if the workaholic is, by turns, detached and snappish. I’ve been through this, as has every other obsessive. It’s difficult to imagine how much more severe it all is for Musk, now in the middle of what he calls the most traumatic year of his career. “Get some downtime" is not the advice he wants to hear; it feels like an invitation to admit failure.

Musk has just two options: to pull through or to crash and burn. That’s not a situation in which any well-meaning advice can be helpful. If he does pull through, though, I’m pretty sure he’ll be able to hit the pillow and satisfy all the criteria of quality sleep, if only for four or five hours. And he’ll face the morning smiling. Winning does that, and I can’t help rooting for him, dark circles under his eyes, 120-hour week and all.

Leonid Bershidsky is a Bloomberg Opinion columnist covering European politics and business. He was the founding editor of the Russian business daily Vedomosti and founded the opinion website