One of the psychological triggers is the challenge/skills ratio. Our attention is most engaged when there’s a very specific relationship between the difficulty of a task and our ability to perform that task. If the challenge is too great, fear swamps the system. If the challenge is too easy, we stop paying attention. Flow appears near the emotional midpoint between boredom and anxiety, in what scientists call the “flow channel” — the spot where the task is hard enough to make us stretch; not hard enough to make us snap.