It is one in the morning on a Tuesday in October. You are in a library carrel near Washington Square, or on a hard chair in a Morningside Heights reading room, or at the kitchen table in an apartment on the Upper East Side, a few blocks from the hospital where you will be back on rounds at six. There are three hundred flashcards left in today's deck. You have read the same paragraph four times.

It usually starts on a Monday. A long weekend of late dinners, a few drinks you did not plan on, one bad night of sleep that turned into three. You wake up puffy, foggy, and heavy, and somewhere between the subway and your desk you decide you need to "detox."

Somewhere around week ten of a marathon build, most runners in New York City hit the same wall. It is rarely the long run itself that breaks momentum. It is everything that happens after it. Your legs do not quite reset before the next hard session