Promises.

You make them all the time and break them on occasion, no doubt. But why does the latter occur when you don’t want it to - especially when the promise you made is to yourself?

Friedrich Nietzsche had a theory about that. The life-affirming Existential philosopher believed it’s because a broken promise usually deals with feelings.

And feelings, my friend, are not truly in your control. They’re involuntary and therefore should not be promised.

Nietzsche wasn’t against all promise making, though.

A promise is an assurance, a type of guarantee. And while it’s impossible to guarantee the involuntary, Nietzsche’s writings stress that your actions are anything but that: that they are always under your power.

So a promise based on doing or not doing something can always be kept, especially when you make it to yourself.

While that last statement may seem obvious, it never crossed the minds of two women engaged in a grocery store conversation I overheard. “I feel I should be getting more sleep,” the one said, “but you know how it is.”

When the other nodded and said, “I feel that way, too,” it took all the restraint I possess not to interject. To explain in no uncertain terms that going to bed is an action fully under anyone’s control - and not quote Nietzsche at length.

Instead, I politely asked them to move their carts so I could continue down the aisle.

But that encounter helped spark this article. So did reading “Sleep Loss and Emotion: A Systematic Review and Meta-Analysis of Over 50 Years of Experimental Research,” a paper that appeared about two weeks ago in the American Psychological Association’s journal, Psychological Bulletin.

Now any paper 24 pages in length that considers 154 studies, uses data accrued on more than 5,700 people, and is written primarily for professionals who study the mind is going to be hard to encapsulate in the witty sort of takeaway I aspire to write. But here’s what I jotted down somewhere in the middle of attempting to understand all the charts and jargon.

That depriving yourself the proper amount of sleep keeps the highs in life low and the lows in life high.

And here’s where I should say that my understanding of the paper was aided by an article about it written by Lisa O’Mary for WebMD. O’Mary spoke to Cara Palmer, PhD, an assistant professor at Montana State University and lead author of the paper, who explained to her that even after short periods of sleep loss - like staying up an hour or two later than usual - the research revealed a reduction in positive emotions, like joy.

“We also found sleep loss increased anxiety symptoms and blunted arousal in response to emotional stimuli,” Palmer said. All of which leads her to declare in the published paper that a “mild deficiency” in sleep leads to “measurable negative changes” in how you react to everyday events.

She does so after citing two studies that estimate more than 30% of American adults and up to 90% of American teens “obtain less than the recommended amount of nightly sleep.” So you can see how Nietzsche’s belief on the fundamental difference between feeling and actions factors into all of this.

If you feel you don’t get enough sleep, do more than express your feelings about it in a grocery store. Act upon that feeling.

And if you’re in need of additional impetus, think about this. Is having an irregular sleep pattern worth dying over?

In a study published in Sleep last September, researchers used data on about 61,000 Brits available through the U.K. Biobank between the ages of 55 and 70 who had worn a device similar to a smartwatch to determine their sleep regularity. They then applied the Sleep Regularity Index to the data, assessed a score, and grouped the scores into fifths.

In a follow-up about eight years later, the researchers found that those people whose scores fell in the bottom fifth were far more likely to have died.

When their scores were compared to all the other peoples’, the researchers discovered the others had up to a 48% lower risk of dying from any cause, up to a 39% lower risk from dying of cancer, and up to a 57% lower risk of dying from cardiometabolic disease, like heart attack, stroke, diabetes, insulin resistance, and non-alcoholic fatty liver disease.

While the study also considered sleep duration, the correlation between all-cause and specific-cause mortality in that regard was not as great, leading the researchers to write that sleep regularity is a “stronger predictor than sleep duration” and “may be a simple, effective target for improving general health and survival.”

So it only makes sense - unless you’re a shift worker - to consistently go to bed and get up at the same times, even if the total time is less than what’s recommended.