to reach a lower energy state, like in chemistry. Big atoms fill in the gaps of another big atom that is quite different, you could say an opposite. Once they share and bond via their nice electrical arrangement, each atom gets smaller.
(I only took chem in college, I'm no chemist so pardon)
But the same is true for men and women, I see it all the time and experience it. Each can't handle trying to deal with the world on their own so they seek each other out, bond, and reach a lower energy state where they no longer care about the wonders of the world and fall into an arrangement of complacent contentment, ever convinced that they are happy in life and need nothing more.