Nothing can save you from your fatigued mind. 

Not time—hours don’t matter when your brain is incapable of making good decisions.

Not money—cash won’t buy you clarity or stamina.

Not relationships—how can you make others happy when you can’t do it for yourself?

If you’ve ever sat in front of the TV to watch something you’ve seen before because you’re tired, you know that time is not your most valuable resource.

If you’ve ever bought anything beyond food, water, shelter, or your other basic needs, you know money is not your most valuable resource.

If you’ve ever wanted to help more people, give more to your current relationships, or build new ones, but were stretched too thin by your current obligations, you know that relationships are not your most valuable resource either.

Mental energy is your most valuable asset. Without it, you won’t have the enthusiasm, motivation, drive, and physical energy to live a full life rich in all of those things listed above.

The problem is this asset depreciates rapidly every day. Scientific studies published in the Harvard Business Review and by Cambridge University Press point to evidence that you only get about 90–120 minutes of peak mental energy and five hours or less of “near” peak mental energy each day.

For the rest of the day, your mental energy levels are medium to low at best. The good news is that if you get enough sleep, your energy replenishes 100%.

A study published in the journal Sleep Medicine reveals that the right amount of REM sleep (four to six cycles) completely restores your mental energy each day. So that’s good, but … Even if you start each day at 100%, your mental energy is going to drop quickly.

That’s why you want to cherish your mental energy. Harvest it. Tend to it like a precious garden. And, when necessary, fight for it.

The fight for your mental energy

Mental energy is the world’s hottest commodity. People are going to try to steal it, drain it, and suck it up every second you’re awake. Yet very few of us protect it. Few of us know how.

People carefully protect the money in their bank account and the time in their calendar, but they do little to protect their attention. Attention is the gateway to your mental energy. Where your attention goes, your mental energy flows.

And more often than not, it is flowing toward something someone else wants.

Taking back your mental energy is not a cakewalk. It’s a dogfight.

Even your own mind is going to fight viciously to keep you distracted.

All the “yeses” you’ve said and all the obligations you’ve taken on in the past have created a kind of “psychological immune system.”

This immune system has evolved to protect your sense of homeostasis. It does so by rejecting any attempts you make to change where you direct your effort. Your brain hates change; it likes distraction. It wants you to stay in this comfort zone of distraction you’ve created, wasting your energy on the wrong things—so it works to keep you there.

Distraction is safe, see?

There are other rewards, too. Your brain likes the approval you get by saying yes to others. It likes the stimulation of drama and gossip. It likes being a small part of everything and a big part of nothing.

You need to repair this immune system.

Protecting your mental energy

Right now, your psychological immune system is seeking safety. You have trained it, either actively or passively, to fear change.

The only way to reprogram it is to start being more selective with where you spend your mental energy. The first step to protecting your mental energy is to ignore the urge to give your attention to whoever or whatever is seeking your attention.

Build up a resistance against this inclination by saying “no” to everything first. This will be hard to do at first but, over time, it will become easier and easier.

Learn to feel a sense of success when you say “no,” rather than a sense of failure.

You’ve been trained since birth to say “yes” to everything. Every time you agreed to do something your parents or teachers told you to do, you received positive affirmation. Now, you see, saying yes is the key to getting rewarded.

This is a mistake. Saying yes without discretion brings failure, not success. Set “no” as your default response. Start rewarding yourself for being selective. Every time you say “no” you get one step closer to achieving true success.

Most importantly, learn to keep all gossip and meaningless drama out of your life. Nothing will drive your mental energy levels down faster than having an emotional blowout. Defending yourself against gossip at the office is tiring; hard work is not. Fighting with your relationship partner is tiring. Falling out with a friend or family member is tiring. Maintaining healthy relationships is not.

The solution is simple—stop burning through your mental energy on emotional drama. The key to doing this is to learn to walk away from energy draining people.

Energy draining people—think of them as vampires needing the energy of others to survive—grow stronger by feeding on your attention. They play the victim, act out, and create all kinds of drama to steal away your attention. Stop letting these people hijack your focus. Protect your mental energy by walking away from them once and for all.

Saying “no” and removing energy draining people from your life will help rewire your brain so that you’re no longer addicted to distraction or drama.

Surround yourself with mental energizers

Once you’ve learned to protect your mental energy, surround yourself with people and activities that increase your mental energy levels.

There are some people and activities you should say yes to, of course. The key is that you need to be selective about who and what you let into your life.

Find people who energize you and keep you on track towards your goals. Then, hold onto them. Find activities that excite you and bring you closer to your goals. Then, keep executing them. These people and activities will ensure that your psychological immune system starts to defend against distraction, and against drama.

Your mental energy is going to plummet throughout the day, certainly. But that’s not a bad thing. It’s only bad if it’s being wasted on people and activities that are pivoting you away from true success. Be selective and start saving your most valuable resource—mental energy—for the best things in life, not the worst.

This is an edited extract from The Science of Intelligent Achievement: How Smart People Focus, Create and Grow Their Way to Success