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But among those 150 people, Dunbar stressed that there are hierarchical "layers of friendship" determined by how much time you spend with the person. It's kind of like a wedding cake where the topmost layer consist of only one or two people—say, a spouse and best friend—with whom you are most intimate and interact daily. The next layer can accommodate at most four people for whom you have great affinity, affection, and concern. Friendships at this level require weekly attention to maintain. Out from there, the tiers contain more casual friends who you see less often and thus, your ties are more tenuous. Without consistent contact, they easily fall into the realm of acquaintance. At this point, you are friendly but not really friends, because you've lost touch with who they are, which is always evolving. You could easily have a beer with them, but you wouldn't miss them terribly, or even notice right way, if they moved out of town. Nor would they miss you.
An exception might be friends with whom you feel like you can pick up right where you left or even though you haven't talked to them for ages. According to Dunbar, these are usually friendships forged through extensive and deep listening at some point in your life, usually during an emotionally wrought time, like during college or early adulthood, or maybe during a personal crisis like an illness or divorce. It's almost as if you have banked a lot of listening that you can draw on later to help you understand and relate to that person even after significant time apart. Put another way, having listened well and often to someone in the past makes it easier to get back on the same wavelength when you get out of sync, perhaps due to physical separation or following a time of emotional distance caused by an argument.
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