You look up and three hours have vanished — that's flow.
The athlete 'in the zone'
Action feels effortless and automatic, self-consciousness gone.
A musician improvising
Fully absorbed, the playing seems to happen on its own.
Deep coding or writing
The right level of hard problem and the world disappears.
Too easy or too hard kills it
Boredom (too easy) and anxiety (too hard) both break flow; the sweet spot sits just past your current skill.
How to spot it in yourself
Set up flow by matching a clear, slightly-too-hard challenge to your skill, removing distractions, and giving yourself a definite goal for the session.
Protect uninterrupted blocks — flow takes ~15 minutes to enter and one notification to lose.
If you're bored, raise the difficulty; if you're anxious, lower it — flow lives on the edge between the two.
You'll forget most of this by next week.
That's just how memory works. Lock flow state in with a 5-minute active-recall session — spaced repetition, no signup.