They develop mental resilience

Do you know who you are after running for 19 hours straight with no sleep? The most mentally resilient people do.

Ultra-marathoner Courtney Dauwalter has managed to stay calm even through bouts of severe nausea, a bleeding head injury, and temporary blindness. She talks about pain as an actual place: she visualizes herself entering "the pain cave." The reason it’s helpful to personify pain is that it serves as a reminder that you’re in control when you enter and equally as aware that you can leave.