Why don't LLM role-playing agents act on their stated beliefs?

Using the Trust Game as a behavioral benchmark, researchers found systematic inconsistencies between LLMs' stated beliefs about how personas would behave and the actual outcomes of their role-playing simulation — at both individual and population levels. Even when models appear to encode plausible beliefs, they fail to apply them consistently.

Key findings: explicit task context during belief elicitation does not improve consistency; self-conditioning enhances alignment in some models; imposed priors tend to undermine rather than improve consistency; and individual-level forecasting accuracy degrades over longer horizons. In-context prompting may struggle to override entrenched model priors, limiting researchers' ability to test alternative theories or correct biases.

This connects to the knowing-doing gap documented elsewhere in the vault. Since Can language models understand without actually executing correctly?, the belief-behavior inconsistency in role-playing is a social-cognitive instance of the same split-brain phenomenon: the model can articulate what a persona would do without being able to enact it. And since Do personas make language models reason like biased humans?, the failure of imposed priors to improve consistency suggests that persona beliefs are not controllable through prompting alone.

Source: Role Play Paper: Do Role-Playing Agents Practice What They Preach?