What is behavioral modularity?

Behavioral modularity is a concept in personal epistemology: Each agent should handle one specific situation — multi-purpose agents are fragile.

Example: You create a 'health agent' that tries to handle sleep, exercise, hydration, posture, and meal timing. Within a week you stop following it because the trigger conditions overlap and contradict. When you're tired but haven't exercised, the agent gives you conflicting instructions. Replace it with five narrow agents — one per concern — and each fires cleanly because each has exactly one trigger and one action.

This concept is part of Phase 21 (Agent Fundamentals) in the How to Think curriculum, which builds the epistemic infrastructure for agent fundamentals.