Hands on a Subway Pole
When I describe the role mathematics plays in my life, I often say that it gives me a set of tools to process and understand the world. One way that manifests itself is that I see graphs everywhere.
For example, when I look at a pole on the subway, I see the distribution of hands that have been on the pole.
I think about things like this because they are interesting, but also because they are practical. Where is the pole the dirtiest, and cleanest? Where are germs most likely to reside? New Yorkers know instinctively to touch as little as possible, but sometimes you have no choice. Best to know your probabilities ahead of time.