I’ve written before about my resolution to Get more sleep, and I’m bringing it up again, because I’m truly convinced that this is one of the first aspects of life to tackle when you start a happiness project.

It’s easy to become accustomed to being sleep-deprived, but it’s not good for you. Many researchers argue that not getting enough sleep has broad health consequences, such as raising your risk for cancer, heart disease, diabetes, and even obesity, but in addition to those, it has a profound effect on your happiness.

One study showed that a bad night’s sleep was one of the top two reasons for being in a bad mood at work (the other? Tight work deadlines). Another study suggested that getting one extra hour of sleep each night would do more for your daily happiness than getting a $60,000 raise.

But here’s another reason why I think sleep matters so much for happiness: exhaustion makes the mornings tougher.

The morning is a hard time for many people.

First, a lot of people try to exercise early in the morning. This is a great idea — you check it off your list and get the mood boost all day long. My weight-training instructor told me, “I’ve noticed that people who exercise first thing are much more likely to stick to an exercise program. If you roll out of bed and exercise, you get it out of the way. If you try to do it later, you come up with excuses for yourself, or other things interfere.”

Second, a lot of people face a gruesome commute. A bad commute is a real happiness challenge, and one to which people don’t adapt. If you’re sleepy, you’re going to be crabby and inattentive, and that’s a bad combination in a driver.

Third, a lot of people have to get their kids off to school. This is why I need a lot of sleep. Every single morning tries my patience to the uttermost. If my big one isn’t complaining, my little one is whining. Remembering to put everything in the backpacks, picking out clothes, finding the right mittens, leaving on time…it’s hard, every day. A lot of my resolutions, such as Sing in the morning and Observe the evening tidy-up, are aimed at improving the morning experience.

I’ve also resolved to “Get up at 6:00 a.m.,” so I have an hour to get myself organized before the rest of my family wakes up. And what does this mean? It means I have to go to sleep earlier.

I was lucky enough to get an advance copy of my friend Erin Doland’s excellent new book, Unclutter Your Life in One Week. It has lots of great information and tips, and I was quite struck by her observation:

“Experience has taught me that to get out of bed just fifteen minutes earlier each morning, most people need to go to bed thirty minutes earlier. To wake up and feel refreshed thirty minutes earlier in the morning requires going to bed a full hour earlier.”

I’d assumed this had just been my idiosyncratic experience, so I was surprised to see that someone else had found the same thing. Alas, I think this is absolutely true.

The fact is, I resent having to go to bed so early, just at the beginning of one of the most enjoyable parts of my day. I finally have an opportunity to read for fun, call my sister in Los Angeles, cruise the internet, or watch TV. Instead, I have to turn out the light.

It’s strange that turning off the light is so hard. You’d think, “What could take less effort than going to sleep?” and yet I find that it sometimes takes a lot of effort to put myself to bed, even when I’m actually feeling sleepy. It’s just so much fun to stay up — or sometimes I feel too tired to take out my contacts.

From 2006 through 2014, as she wrote The Happiness Project and Happier at Home, Gretchen chronicled her thoughts, observations, and discoveries on The Happiness Project Blog.