My first marathon went exactly as planned from the start of training to the finish line. I found the perfect pair of running shoes , weekly mileage increases had me feeling strong, and the day of the race was sunny and cool. Running down the final stretch to the finish line felt more like flying, and afterward I took the best nap of my life. It was the perfect end to the perfect training block. Call it beginner’s luck.

I ran the New York City marathon last fall and had a totally different experience. While actual race day rocked, training was fraught with injury. Nothing severe or dramatic, of course, just enough nagging pain to keep me up at night scouring Google and Reddit to compare symptoms and calculate recovery times based on anecdotes.…