Is the bus coming?

I planned to take a bus back to the hostel from Vatican City. I went to a nearby bus stop and began waiting. The bus I wanted went by several times in the other direction, so I knew it was running, but it never showed up on our side. We were probably passed by 15 other buses, but never the one I needed. It was one of those situations where you say to yourself "if I leave now, the bus will probably show up right after I leave." After about an hour of waiting I gave up and walked a few blocks back to the subway. I really never figured out why the bus never came.