On some subway stations you can exit the train on both sides. One side usually leads to the exit, the other door is the right one if you want to catch the train in the opposite direction.
If you are travelling on your own, it’s easy. You are the one to decide what is the right door for you. But if you have company and you doesn’t sync with the other person it might happen that you exit on the left side and your company on the right side. As soon as the train is gone you realize that now there’s a gap between you. Too wide to jump. Too bad.
You can wait for the next train and use it as a bridge to the other side or you can exit and walk all the way to the opposite entrance. The first option means you have to wait, the second one might be exhausting.
But first of all both of you have to make sure who is on the wrong side of the platform.
PS: Because of a business trip there won’t be a new posting until Friday.