You look up, and it’s you. Exiting the library, walking down the Quarter Mile, you watch them as they slide by unnoticed.
You have met your doppelgänger.
While before you lived your life in peaceful ignorance, there is no going back. Now that you have noticed them, they will turn up seemingly wherever you go. Slowly, your doppelgänger becomes aware of you as well.
Then it is a matter of avoiding eye contact while brushing past each other in the hallways. It is a tangible awkwardness, as if the universe is realizing its mistake. Two humans, exactly alike in looks, is a statistical improbability...