Some of the most striking documented examples of flow come from people enduring extreme deprivation — solitary confinement, prison camps, isolated captivity — who kept their minds intact by deliberately constructing rule-bound mental activities out of almost nothing. This suggests flow isn't merely a pleasant enhancement to an already good life; under the right conditions, it functions as a genuine psychological survival mechanism, imposing order and purpose on a situation that offers neither externally.
What these cases share structurally is deliberate self-imposed structure: a goal, a set of rules, and a way of tracking progress, invented entirely from within because the environment provided none of it. The lesson generalizes past extreme circumstances — the same principle (imposing your own structure, goals, and feedback when the external environment gives you none) is available in far more ordinary situations of enforced waiting, isolation, or unstructured time.
A WWII prisoner held in Nazi solitary confinement, Christopher Burney, deprived of nearly all stimulation, kept his mind occupied by spinning long chains of association from the few objects in his cell. Ceramic designer Eva Zeisel, imprisoned over a year in Stalin's Lubyanka prison, invented mental games — imaginary chess, conversations with herself in French, composing and memorizing poems. Albert Speer, imprisoned at Spandau, spent months mentally walking from Berlin to Jerusalem, tracking imagined towns and landscapes along the route. And an American Air Force pilot held for years in a North Vietnamese jungle camp mentally played a full round of golf every single day of his captivity — choosing clubs, varying the course in his mind — and upon release, weakened and malnourished, surprised fellow officers by playing an excellent actual round.