A funny thing my wife and I noticed while hiking is how friendly people are on the mountains, often saying hello as we pass each other, but this friendliness basically always stops as soon as we leave the trail. Of course, on the practical side, if you say hello to someone you are more likely to remember them, which could prove useful if someone got lost, while in crowded streets it would be very tongue-tiring to say hello to everyone!
I often travel by bicycle to go to work and today was no exception. On my way back from my Wednesday morning job, I recently started seeing this jogging woman who always says hello. This morning I told myself I had to ask her for a picture, and although surprised, she readily agreed. Hello to you!