PYEONGCHANG, South Korea — Karen Chen found herself in a room full of athletes, and she froze. Chen, 18, describes herself as a “shy kid,” and her nerves were getting the best of her again. She was there hoping to trade collectable pins, a longstanding Olympic tradition that helps break the ice between people from different sports or countries. She just couldn’t do it. “I was nervous,” she said. “Like, ‘What if this person doesn’t want to trade pins with me?