Flow state (Csikszentmihalyi) is the psychological state of complete absorption in an activity, where the task's challenge perfectly matches one's skill level.
Mechanism: Transient hypofrontality (prefrontal cortex quiets), heightened dopamine, norepinephrine, anandamide, and endorphin release. Time perception distorts. Self-referential thinking drops.
Use case: Engineer the conditions: high-challenge / high-skill match, clear goals, immediate feedback, freedom from interruption, deliberate triggering (start ritual, music, environment).
Caveats: Flow is a state, not a strategy. Chasing it instead of doing the work backfires. Show up; sometimes it shows up too.