Often, photographers are attempting to find symmetry or patterns within their environment that would be eye catching. This picture is a great example.
I was standing in the airport waiting to get on one of the trains and noticed the adjacent train sitting there. I noticed the ceiling tiles, train doors, windows, floor tiles, and even the trash can all had a similar linear pattern. I felt this would be a great place to focus on the train and hope that a subject would walk through. Fortunately, I got lucky. This man carrying a piece of paper walked right where I wanted him. I love that I caught him in mid stride because his front leg, back foot, upper torso, and paper all became symmetric with the environment. By focusing on the train, I was able to blur the subject so the viewer could get a sense of motion.