A few weeks ago, I chatted with a smart, successful startup founder for a story I was working on at midnight his time (I'm not the world's rudest journalist -- that's when he called me). After the call I had a nonurgent follow-up question and emailed him expecting an answer when he woke up. He got back to me at 4:30 a.m. When do you sleep, I jokingly asked in my reply.

His answer: Sleep is for my competitors.

I'm sure he's far from the only entrepreneur who feels this way, but it was this particular founder I first thought of when I read a fascinating recent Medium post from author David Kadavy. The piece contains fragments of a recent interview Kadavy did with neuroscientist John Kounios on the topic of -- you guessed it -- sleep.

"Sleep is mental work."

Here's the money quote: "Sleep is not doing nothing. Sleep is mental work. Sleep is creative work. Your brain is churning over memories, it's clearing out the mental cobwebs--it's generating ideas. Sleep is itself work. So if a person's trying to solve a problem, and they take a nap to sleep on it, that's not not working on the problem, that is working on the problem."

The post goes on to explain the finer points of exactly what your brain is working on while you're snoozing away (short answer: memory consolidation). It's well worth checking out if you find that kind of thing fascinating (or, for the real deep dive, Kadavy is offering a podcast of the complete interview), but for those like my recent source who are inclined to view sleep as wasted time, this single quote should be enough to get them thinking.

When you tell yourself, "I don't have time for sleep. X, Y, Z task is more important," is that really true? Is X, Y, Z really more critical than keeping your brain functioning optimally? More important than generating new connections and associations (also known as creative ideas)? Sleep isn't nothing. It's essential mental housekeeping.

Kadavy's post also reminded me of a similar argument about vacations from Y Combinator alum and Amicus founder Seth Bannon. It uses similar logic. You might think sitting on the beach reading a page turner is clearly less critical than meeting one more client or closing one more deal, but Bannon urges entrepreneurs to rethink how they value time off. It's not nothing. It's actually an essential part of your job.

"Professional runners take long breaks between marathons. They make no excuses for this, and no one judges them for it, because everyone knows that rest and recuperation is an essential part of being a pro athlete. The same is true for entrepreneurs (and everyone, really). Preventing burnout is part of your job. Staying well rested is part of your job," he insists.

Are you wildly undervaluing sleep and rest?