You’re lying on a sandy beach near the historic Hotel del Coronado in beautiful Southern California. Nearby are the friends who’ve spent the past two weeks with you on the white sand and in the jade-tinted water. It’s 3 a.m. You’ve crawled to this spot after thirty minutes of kneeling in the sand at the wave line, as cold surf pounded your body. You’re soaking wet and shivering uncontrollably. Your hands are chapped raw. Every muscle in your body is filled with painful lactic acid from uninterrupted exercise drills over the past sixty hours. You hear a man scream through a bullhorn that you should quit this group—give up—and enjoy the warm ...

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