I find this saying to be one of the wisest I have come across in my reading and thinking. I have blogged on it previously (see link).
The saying is very applicable to discussions of public policy--for example, when someone opposes school vouchers because vouchers do not fix all of the problems of education. Yet, the saying is also very applicable to what I call "private policy": how we relate and "connect" to others.
Our oversexualized Western culture, for example, diminishes the opportunities for platonic friendship between the sexes because casual sexual activity has become so common that every man-woman relationship becomes fraught with the inevitable sexual question. People become anxious and fail to expand their network of friends because the good (platonic) becomes lost in obsessing about the perfect (the ultimate romantic and sexual relationship). That obsessive focus on the "perfect" can trigger emotional panic and anxious withdrawal in not a few people. Ironically, the supposedly "care-free" sexual revolution has made social interaction more "uptight" since everything is up for grabs at all times in all circumstances.
A saner and more sensible view of life would run along these lines. It takes a village, a network, an oikos or "extended household" (to use the Greek) for all human beings to flourish. Different individuals can play limited roles; but when you add them all up, you get a full life. Hyperindividualistic Western culture with its emphasis on sexual activity, cohabitation, and other obsessive and excessive behavior cheats us out of that more sensible and balanced view of life. It is a shame because a balanced approach is ultimately more fulfilling. A balanced approach also gradually forms us into human beings mature and restrained enough to find the ultimate relationship that is best for us.
(The Vermeer painting of a woman holding a balance is in the public domain.)