Prioritizing what's important is challenging in today's world. The split focus required to maintain a career and a home, not to mention a Facebook feed, can feel overwhelming.

Enter the science of what to prioritize, when.

For over 75 years, Harvard's Grant and Glueck study has tracked the physical and emotional well-being of two populations: 456 poor men growing up in Boston from 1939 to 2014 (the Grant Study), and 268 male graduates from Harvard's classes of 1939-1944 (the Glueck study).

Due to the length of the research period, this has required multiple generations of researchers. Since before WWII, they've diligently analyzed blood samples, conducted brain scans (once they became available), and pored over self-reported surveys, as well as actual interactions with these men, to compile the findings.

The conclusion? According to Robert Waldinger, director of the Harvard Study of Adult Development, one thing surpasses all the rest in terms of importance:

"The clearest message that we get from this 75-year study is this: Good relationships keep us happier and healthier. Period."

Not how much is in your 401(k). Not how many conferences you spoke at--or keynoted. Not how many blog posts you wrote or how many followers you had or how many tech companies you worked for or how much power you wielded there or how much you vested at each.

No, the biggest predictor of your happiness and fulfillment overall in life is, basically, love.

Specifically, the study demonstrates that having someone to rely on helps your nervous system relax, helps your brain stay healthier for longer, and reduces both emotional as well as physical pain.

The data is also very clear that those who feel lonely are more likely to see their physical health decline earlier and die younger.

"It's not just the number of friends you have, and it's not whether or not you're in a committed relationship," says Waldinger. "It's the quality of your close relationships that matters."

What that means is this: It doesn't matter whether you have a huge group of friends and go out every weekend or if you're in a "perfect" romantic relationship (as if those exist). It's the quality of the relationships--how much vulnerability and depth exists within them; how safe you feel sharing with one another; the extent to which you can relax and be seen for who you truly are, and truly see another.

According to George Vaillant, the Harvard psychiatrist who directed the study from 1972 to 2004, there are two foundational elements to this: "One is love. The other is finding a way of coping with life that does not push love away."

Thus, if you've found love (in the form of a relationship, let's say) but you undergo a trauma like losing a job, losing a parent, or losing a child, and you don't deal with that trauma, you could end up "coping" in a way that pushes love away.

This is a very good reminder to prioritize not only connection but your own capacity to process emotions and stress. If you're struggling, get a good therapist. Join a support group. Invest in a workshop. Get a grief counselor. Take personal growth seriously so you are available for connection.

Because the data is clear that, in the end, you could have all the money you've ever wanted, a successful career, and be in good physical health, but without loving relationships, you won't be happy.

The next time you're scrolling through Facebook instead of being present at the table with your significant other, or you're considering staying late at the office instead of getting together with your close friend, or you catch yourself working on a Saturday instead of going to the farmer's market with your sister, consider making a different choice.

"Relationships are messy and they're complicated," acknowledges Waldinger. But he's adamant in his research-backed assessment:

"The good life is built with good relationships."