These are natural growths. If the first interview between two persons is agreeable, they both look for an opportunity to repeat it; if it is disagreeable, they avoid repeating it, provided there are other more congenial companions accessible at the time when companionship is desired. A specially attractive person may find many groups competing for his presence, in which case his inclinations naturally lead him to the one or two which most satisfy his needs; he keeps himself out of the others, not necessarily because he hates them, but because there is not enough of himself to go around. A strong group lasts until something happens to break it up; some hindrance arises to meeting, a member moves away or finds another group more attractive, or a careless remark is made that gives offense. The friendship mentioned below was only the most congenial acquaintance out of the large number which the young lady who reported it engaged in:

Accidentally meeting a girl at a house-party four years ago, I found in her a friend whom I think more of than any one else outside of my family. I did not plan to meet her or to cultivate her acquaintance. Our friendship simply grew until it means much to both of us.