The Hermit is nine, searching alone; the Wheel of Fortune is ten, and the outer world starts turning. A wheel hangs in the sky with creatures rising and falling on it, and in the four corners the emblems of the four evangelists — four fixed points around a circle that never stops. That's the mechanism: change is the constant, and the only thing that doesn't change is that it will. Ten in the minors is fullness and the turn of a cycle; in the majors it's the journey's midpoint, and outside force stepping in.
Where you'll recognise it: the situation shifting without your having done anything, opportunity or trouble arriving for no reason, the sense that 'it's time'. This card is about the layer you don't control — the wheel doesn't obey you, but you can decide which spoke you're standing on.
Running well, the Wheel is the most favourable state there is: timing right, things linking on their own, effort finally caught. Stuck, its problem is believing the wheel will stop — thinking good will stay good, thinking bad has no exit. The four corners mean this: the wheel turns; the one watching doesn't have to turn with it.