On a crowded platform, try it on three people. The man with the wet umbrella. The woman rereading the same message. The teenager who is clearly late for something. Wish each of them a good year, silently, and move on.
Nothing visible happens. What changes is on your side: for about a minute, a station stops being an obstacle course full of people in your way and becomes a room full of separate, complicated lives. That shift is not nothing. Most unkindness begins with the obstacle-course version.