Final answer:
Sadie is engaging in 'emotional labor' or 'emotion regulation' to maintain a positive image in front of parents, friends, and classmates after losing a tennis match.
Step-by-step explanation:
Sadie's behavior after losing the tennis match, where she displays a happy facade despite being sad, is reflective of emotional management and social expectations. This action of masking one's true feelings in a social context, often to adhere to certain norms or to avoid negative perceptions from parents, friends, and others, is known as 'emotional labor' or 'emotion regulation'. It's an effort to maintain a positive public image and is linked to the psychological concept of 'self-presentation'.