A little C.S. Lewisesque thought, brought on by a rather providential occurrence this morning:

Never, ever, ever shrink from greeting the strangers you bump into, and heartily return a greeting when given one from another. It may brighten their spirits; yours will be, too, undoubtedly. I have seen it so many times. Happiness begins the day we lose our nagging sense of shame for being refused, by an occasional grump, the fellowship of informal acquaintance.