Money can buy a lot of things that make your life better. Like, oddly enough, time.

According to a 2017 study published in Proceedings of the National Academy of Sciences, people, regardless of socioeconomic status, who were willing to spend a little money to have others perform tasks they didn't enjoy or want to do -- like mowing the law, cleaning the house, or running errands -- were happier and felt greater overall life satisfaction than those who did not.

No matter how much you make, no matter how wealthy you are, buying a little time makes you happier. (Granted, with a couple of catches.)

So, yeah: Money can buy a lot of things.

But not fitness.

Not diet.

And not meaningful relationships.

Why does that matter? If you need a bottom-line reason, fitness can play a major role in your success. Exercising at moderate intensity for 20 minutes can elevate your mood for up to 12 hours. Exercise can improve your memory and cognitive skills. Exercise can help you better manage stress.

The same is true for diet. Not being on a diet, but eating a reasonably healthy diet. (Which I realize can sound like the same thing.) Research shows that eating poorly leads to a lack of sleep. Eating poorly decreases what social psychologists call "helping behaviors" and increases "withdrawal behaviors" (basically, avoiding other people.) Eating poorly can impair decision-making.  

And as for relationships? A study of over 300,000 people found that people with a few close friends have a 50 percent higher rate of longevity than those with "weaker" ties. The key is to have three or four really, really good friends, and then, of course, plenty of people who aren't necessarily friends but are fun to be around, or result in a mutually beneficial relationship, or share common interests.

None of which you can outsource.

Or buy.

No matter how much you make, you can't pay someone to exercise for you. Or eat healthy for you. Or nurture close relationships for you.

Those are up to you.

Which is a good thing, because no matter your circumstances, health and relationships can be your competitive advantage. Exercise improves almost every aspect of your life: your body, your mind, your confidence, your willpower -- everything.

Same for diet.

Same for close relationships, especially if you choose your friends wisely. Research shows that becoming friends with people who exhibit the traits you wish to possess makes it much more likely you will succeed. Research shows that becoming friends with people who make steady progress toward goals will improve your willpower and determination.

Make and keep a few close friends, and you'll likely live a longer life.

And live a happier, more fulfilled, more successful life.

Exercise, diet, and relationships? You can't pay -- or rely on -- other people.

And that's a good thing.

Because it also means those are aspects of your life that you can totally control.