Money is important. Time is important. But these are not the quantities that will limit you in your life.

Without energy, neither of these factors means very much; nothing really does. Think about it: you could have a huge bank account, but it won’t matter one bit if you’re confined to your bed with glandular fever and unable to stand up straight, let alone spend and enjoy that money. You could be young, bright and full of promise, but if you’re depressed and lethargic 100 percent of the time, all that youth and potential means nothing. Without energy and the capacity for action and execution, all of your best intentions won’t matter a lick.

This is a book about the psychological and physiological bases of energy—where it comes from, how we can maintain it, and how to get more of it. You can think of energy as the most primordial, fundamental kind of wealth. Energy—whether it’s psychological or physical—is like your personal fund of life itself. It’s the well that you draw all your motivation, enthusiasm, and passion from. It’s what makes one person’s life a boring slog while another person, doing much the same thing, appears to be living with zest and purpose.

It all comes down to energy. There’s a great big world out there, and if we’re to explore it, we need the physical and emotional strength to get out there and engage with it. Opportunities abound all around us, but if we’re too depleted and uninspired to grab them when they do, it doesn’t matter how fortunate we are or how many lucky breaks come our way.

It’s a little like having the world at your feet, and a map of this world’s awesome highways and roads in front of you, but not having any fuel in your car. Without energy, life becomes two-dimensional and gray. You may even feel like life is just whizzing past you, and you’re left behind because you can’t keep up.

When we have energy, the world is ours. We have the spirit and the wherewithal to grasp it. We can reach out and engage with others, with our environment, with ourselves, with our dreams. We have what’s needed to build our ideal world, one brick at a time, and we have the resilience and spring in our step to appreciate what we already have. Energy is fuel—it powers everything great in life, whether that’s creativity, productive work, innovative solutions to life’s problems, personal development, rich relationships with others, or simply the joy of having a strong body, a clear mind, and robust emotional health.

The great thing about energy is that in some ways, it can feed on and encourage itself. When you are energized, you act decisively and with conscious intention. You turn down distractions or temptations. You’re able to push yourself a little, and grow because of the challenge. And when you grow, you’re inspired to keep going, setting up today the conditions that will most benefit you tomorrow. Acting with energy has a cumulative effect, bolstering you against life’s trials and difficulties, and making celebrations and triumphs all the more wonderful.

Unfortunately, the opposite is also true. Low energy creates more apathy, more tiredness, more of that listless “blah” feeling that only seems harder and harder to budge the longer it lingers. When you’re low on energy, you’re more likely to take the easy way out, give up on your dreams because they’re too challenging, or put up with negative behavior in yourself and others that you might not have otherwise. The result is a steady stream of self-reinforcing behaviors that create a compromised life that just feels bad, plain and simple.

This is why it’s so important to focus on energy. It doesn’t matter how many other great things you have going on in your life; if you don’t have the energy to engage with them properly, to appreciate them, to bring them to life, it’s the same as not having those great things at all.

In a way, we can think of this as “multiplying by zero,” a mathematical mental model that preaches the importance of shoring up your weaknesses. In mathematics, it doesn’t matter what else is going on in an equation or expression—if you’re multiplying by a zero anywhere, the end result is always the same: zero. You might think you’re onto the next big mathematics discovery like Pythagoras or Descartes, but if a zero slips in there without your noticing, you’re just going to end up with a fail for the day. No amount of finagling or negotiating will impact your result.

And so lack of energy is like the big fat zero that cancels out all your other efforts and intentions, no matter how grand and noble they may be. In fact, you could do your best to keep on increasing the other variables as much as you wanted (for our purposes, well-wishing, hoping, dreaming, good intentions, and self-flagellation), but it wouldn’t matter. Even infinity multiplied by zero is still… zero.

A chain, as they say, is only as strong as its weakest link. Even if all the “links” in your life are looking pretty good, they can’t do much about that one wobbly link, that “zero” that can break and undermine the strength of the entire chain.

In this book, we’re going to first examine ways to make sure your energy quotient is a non-zero, and in fact, is always one of the most powerful variables at your disposal. Soon after, we’ll focus on optimizing the rest of the equation, learning to beat procrastination, creating better goals, and manipulating our psychology to be more effective and efficient. Often, you’ll find that increased energy is the true cure to what ails you because it allows you to have willpower, dig deep, and reach goals. That’s the real secret behind traits like self-discipline and resilience.

Let’s consider a real-life example. Since you can remember, you’ve wanted to write that special novel about cats and murder on the Hawaiian island of Oahu. You have so many big ideas, a real message you want to share with the world, but somehow it never comes together. You wake up in the morning and promise yourself you’re going to find time to sit and write today. You can barely sit still because of your anticipation over plotting, character development, and the invention of a new fantastical language (for the cats, obviously). But then after a hard day’s work, after your commute home, after housework and just, well, life, you’re exhausted. Suddenly, you don’t feel quite so inspired. You put off your Great Novel Dream until tomorrow. Tomorrow becomes next week, and then next month. And so it goes.

Let’s run through a list of common recommendations for someone in your current position of struggling to write a novel. You could try and take other people’s advice on how to write your book. You could read about making better plans and outlines, or join a writing group, or even hire a writing coach to help you out of your “writer’s block.” These recommendations try to improve or optimize other variables in the equation, but they don’t address the real problem. You don’t have writer’s block, and you don’t need a coach. You’ve just run out of energy, and you’re trying to multiply by zero. And again, when your energy’s at zero, none of that other stuff matters. So long as that’s the case, you’re going to keep coming up short when it comes to things that you really care about.

When you zoom out and take a bird’s-eye view, you can see so much of what’s out there in the personal development realm as merely the hopeless attempt at increasing numbers in the rest of the equation, without doing a thing to increase that big fat zero that will cancel it all out. You could waste unbelievable amounts of time trying to understand the psychological, cognitive, institutional, behavioral or maybe even spiritual dimensions to why you can’t achieve the things you’ve already identified as important. But there’s a pretty simple explanation that will help you understand all of this without resorting to all these theories: you’re tired. You simply ran out of energy. Your gas meter is out; your battery needs recharging.

After all, at the end of the day we are all biological beings; we’re all organisms that need energy to work, to move, to communicate, to live. If that aspect isn’t working well, all the rest of it is utterly irrelevant. So, it’s no use talking about motivation or passion or inspiration, or even deeper things like life purpose and vision, if you’re exhausted and have already burnt all your life “fuel” for the day.

With this in mind, let’s turn our focus from the rest of the equation and learn more about the one element that is quietly undoing all of your effort: that tiny zero that nevertheless has a big impact. We can break down energy—psychological and physiological—into four general categories, and this is well-represented by the concept of the energy pyramid, as put forth by Tony Schwartz.