I've been left behind many times. The main one that pops into my head was when I was in 3rd grade. My brother and I went to a private Catholic school, and after school we had to ride a bus to the local high school and THEN get on a high school bus to get home. Our bus was late, and when my brother found it, he thought I was with him, but I wasn't. The buses all left, and I couldn't find anybody I knew. my brother soon realized that I wasn't on the bus, but he couldn't get the driver to turn around and get me, and THEN the driver wouldn't let him off the bus so he could come back to me.
There are many more stories, and to this day, if I'm in a store with someone, I have to know where they are at all times because if I can't find them, I start to panic because I think they've left me. It's really quite sad.