The Short Version
Mostly True. Peer-reviewed research consistently shows that a person's mindset shapes their observable behavior — facial expressions, tone, body language, and communication style — which in turn influences how others perceive and respond to them. However, the claim oversimplifies the mechanism: people do not detect mindset directly but react to behavioral cues and their own interpretive biases. The effect is also probabilistic and context-dependent, not universal or deterministic.