Social groups are structured in a series of layers
We have also found that human social groups are structured in a series of layers that extend out beyond the 150 number, and these layers have a very specific relationship to one another.
Generally speaking, humans each have one to two special friends, five intimate friends, 15 best friends, 50 good friends, 150 “just” friends and 500 acquaintances. Our relationships form a series of expanding circles of increasing size and decreasing intensity and quality of the relationship. Not only do we see these circles in the structure of [modern, real-world] social networks and of hunter–gatherer communities—they’re also reflected in big data gleaned from Facebook posting and telephone call frequencies.
It also turns out these layers are germane to the organizational structure of modern armies.(…) Company size in the British army is 120 troops, and it’s 180 in the American army. These sit nicely on either side of 150, the number of friends per person my research identified. There’s just something special about these numbers, something to do with the structure of relationships that makes them very stable. Even the number of “intimate friends” is reflected in the size of special forces units. For example, British Special Air Service squadrons have four men each.
We do not love people so much for the good they have done us, as for the good we do them.
Love does not consist of gazing at each other, but in looking outward together in the same direction.
It is not a lack of love, but a lack of friendship that makes unhappy marriages.