Most regular games have five players. Four sit down to play; the fifth person pulls up a chair just far enough back to see every rack without hovering. She scores, she refreshes drinks, and she waits for the next round.
At first the fifth chair feels like a consolation prize. You are not really in the game. But after a few evenings you realize it is the best seat in the house. From there you can watch three hands at once: the discards, the exposures, and the small gestures that reveal whether someone is one tile away or just pretending to be. You see how a hand changes when a player gets nervous, how a safe discard becomes a gift, and how often the winner was not the person with the best tiles but the person who paid attention.
The fifth chair is also where patience lives. You cannot touch the tiles, so you stop solving and start noticing. You learn that mahjong is less about the hand you were dealt and more about the story the table is telling. By the time your next round arrives, you have already read half of it.