Guard Gwen

She made students feel the consequence in the sliding phase.

"Say your opponent has just closed a mill and it's their turn to capture. They look across your board for a piece to take — and they find that half your pieces are tucked inside mills of your own, untouchable. They can only take a piece that is NOT in a mill. So the pieces you leave exposed — the runners, the loose stones between formations — those are the ones that bleed. The lesson: when you know a capture is coming, tuck the pieces that matter inside mills, and leave only the pieces you can spare standing in the open."

The subtext, older students caught, was about where you place what you can't afford to lose — that the same structure that lets you act can be the thing that keeps you safe.

But Gwen was scrupulous about the exception, because it had cost her a game once.

"There's an 'unless,'" she said. "A piece in a mill can't be captured — unless every single one of your opponent's pieces is also in a mill. Then the rule lifts, and any piece may be taken. Because otherwise a player could wall up all nine pieces into overlapping mills and become completely uncapturable — the game would freeze forever. The loophole exists to stop the perfect turtle. If you've hidden everything inside mills, you've hidden nothing — the protection turns off precisely when you'd need it most."

She drilled the practical judgment with a position: the student, about to be captured, had two pieces exposed and had to decide which to shelter.

"Both are outside mills right now," Gwen said. "You have one slide before their capture. You can move one piece into a mill and protect it, but not both. Which do you save?"

The student studied it. "This one," she said, "the keystone — it's on two of my almost-mills. If I lose it, both collapse. The other exposed piece is just a spare runner; losing it costs me a step, not a plan. So I slide the keystone into the mill and shelter it, and let them take the runner."

"Good," Gwen said. "You didn't try to save everything. You can't. You saved the one whose loss would break you, and you paid the small bill on the one you could spare. Protection is a scarce resource — spend it on what matters."