Coincidence: I’m flying to Miami last week. Sort of weird guy sits next to me. We don’t talk much, but I notice him. We land. I go to my hotel, have an hour to spare before my speech, go to the gym to work out. He walks in.
Coincidence: Last night, I’m flipping through a really old reference book from when I used to write trivia questions. Spend five minutes reading the entry on Gary Glitter who I confess I had never heard of. Today, on the radio, I hear he’s being reprieved and let out of a Vietnamese jail early.
Coincidence: I’ve had my cell phone for two years. I have never once received a text message. Two weeks ago, I sign up for Facebook (long story) and need to confirm my ID by using my cell phone and a text message. In the last 10 days, I’ve received more than ten text messages, all commercial.
Reason 1 you need to worry about coincidence: human beings want explanations, even for totally random events. So they make up stories. If those stories are about you (I have no proof that Facebook is selling my number) then you have to live with that.
Reason 2: if you can cause coincidences to happen, people are going to talk about you. And that might be a good thing.