American Heart Association CEO Nancy Brown reviews ‘Thrive: The Third Metric to Redefining Success and Creating a Life of Well-Being, Wisdom, and Wonder,’written by Arianna Huffington, co-founder of The Huffington Post. Brown has a weekly column that appears on the popular website.

You’re just about to turn out the light and start getting that much-needed sleep you’ve been craving for hours. Then you come to a screeching halt. You remember that one last item on your to-do list that didn’t get done. As you yawn for what seems the 100th time in the last hour, you start calculating: If you don’t take care of it right now, it’ll be yet one more thing to get done tomorrow. And you already know there is going to be a lot on your plate when the alarm clock sounds.

So instead of clicking the off switch, you decide that the sensible thing is to get back to business.

All of us have busy days, and sometimes we have to put in an extra effort to get the job done. But as study after study has shown, we all have our limits and we ignore them at our own risk. The physical and emotional stress of maintaining a nonstop schedule can end up being counterproductive. Having a healthy sense of balance means knowing when it’s time to hit the off switch.

No one has a better grasp on the need for balance than my friend Arianna Huffington. Arianna has always been a firm believer in the power of hard work, a core personal value that has played a major role in her success as an author, political commentator, co-founder in 2005 of The Huffington Post, and mother of two daughters. But in her brilliant new book, ‘Thrive: The Third Metric to Redefining Success and Creating a Life of Well-Being, Wisdom, and Wonder,’ Arianna warns that while burning the candle at both ends can be a fast-track to career and financial achievement (which she refers to as the two conventional metrics of success), it’s important not to neglect her third metric, physical and emotional well-being.

In the early days of The Huffington Post, Arianna was maintaining 18-hour work days to stay on top of things. Her efforts clearly paid off, as the website grew into one of the world’s most popular online destinations. Along the way, however, Arianna lost her personal sense of balance, and was paying a heavy toll. In 2007, as exhaustion set in, she realized she needed to step back and re-evaluate her approach.

“The reality was, I couldn’t do it all,” she said.

None of us can do it all, nor should we expect to.

Last week, as a guest on the Ellen DeGeneres Show, Arianna talked about several of the healthy changes she’s made, which include getting more sleep, meditating, “disconnecting” from digital devices and making time every day for conversation, hobbies and other activities that heighten our sense of joy in life.

“If we sacrifice our health and well-being, then what do we really have?” Arianna asks.

Arianna speaks with the wisdom of experience and the sincerest desire to help others live healthier and more fulfilling lives, and that’s what made it such a powerful reading experience for me. As she reminds us, I challenge you to stop and look at the big picture. It’s easy to get stuck on a “treadmill,” whether we’re trying to move up to the next rung of the career ladder or simply complete our daily to-do list. Step off that treadmill, look around and breathe in the fresh air.