"Acquaintances are always abundant; friends are always scarce!"

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The dividing line [between friends and acquaintances] is communication, I think. A friend is someone to whom you can say any jackass thing that enters your mind. With acquaintances, you are forever aware of their slightly unreal image of you, and to keep them content, you edit yourself to fit. Many marriages are between acquaintances. You can be with a person for three hours of your life and have a friend. Another will remain an acquaintance for thirty years.

— John D. MacDonald