There are no rules for friendship. It must be left to itself. We cannot force it any more than love.
—Hazlitt.
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There are few subjects which have been more written upon, and less understood, than that of friendship. To follow the dictates of some, this virtue instead of being the messenger of pain becomes the source of every inconvenience. Such specialists, by expecting too much from friendship, dissolve the connection, and by drawing the bands too loosely at length break them. It is certain that the best method to cultivate this virtue, is by letting it, in some measure, make itself; a similitude of minds and of studies, and even sometimes a diversity of pursuits, will produce all the pleasures that arise from it. The current of tenderness widens as it proceeds; and two men imperceptibly find their hearts filled with good nature for each other, when they were at first only in pursuit of mirth or relaxation.
—Oliver Goldsmith.