Anyhow, it is a good quote and an interesting one. It suggests that one of the reasons for keeping people close to us is that we don't trust them. Is this the only reason why we wish to keep people close? I'm going to argue that it is, although I could be wrong. Take the titi monkey as described by Helena Cronin in a recent article on the battle of the sexes. As she writes:
"Picture a pair a titi monkeys, husband and wife, in close embrace, their tails entwined, in sleep cuddled together, when awake always close preferring one another's company above that of all others."
It just seems so cute, so human, so much like being in love, so much like close friendships (with the possible exception in the latter case of cuddling together during sleep, but I might be displaying old fashioned attitudes here). She then goes on to explain that the reason for this behavior is that each is party is protecting its investment. The male is making sure that no other male reproduces with his mate whereas the female is making sure that her mate doesn't run off and shirk his childrearing responsibiltities (male titis happen to invest a lot of effort rearing the kids). Titi 'love' -- and why not call it that? -- is fundamentally based on mistrust.
Keeping friends close, then, could simply be a way of ensuring that they will return our investment in them (emotional, material, etc.) rather than their going off and giving it to someone else. The rather wonderful Carl Bergstrom has, in fact, proposed that when friends 'hang out' together apparently wasting time, they are in fact keeping each other close; each making sure that the other isn't off hanging out with others.
As relationships mature, of course, we come to trust our friends and partners and we give them more freedom. As Sting so rightly sang, if you love someone set them free (which, as it turns out, he plagiarised from American novelist Richard Bach). Why might increased emotional closeness lead to our giving our friends and partners more freedom? The economist Russell Hardin might have the answer: we trust someone to the extent that their interests encapsulate ours. We believe that they would not betray us because betraying us would be to betray their own interests. A successful courtship -- whether that be romantic of becoming friends with someone -- is a process whereby we identify interests and maybe even 'grow together' in the sense that our interests become increasingly aligned and entwinend. The closer are the interests, the lower the likelihood that either party will defect on the other (see my earlier posts on homophily and trust).
That's not to say that we can ever trust anyone 100%. No matter how perfectly my interests might overlap with yours I'm still here in this body and you are still there in yours and that is a fundamental conflict of interests that can never be breached. But Michael Coreleone or Sun-Tzu or whoever it was was right: you do not need to keep your friends close, because they are always close you've chosen them because they have your interests at heart and, if you've done your job properly, you've planted in them the goal to act for you. Just like they have with you.