Reversi

Flank the CPU's discs to flip them to your colour. Hold the corners and own the board when it fills.

Reversi was invented in England in the 1880s; the Othello name and the standardised starting position came from Goro Hasegawa in Japan in 1971. The board is 8×8 and the discs flip, which makes material a uniquely unreliable guide.

The counterintuitive principle is that having more discs in the midgame is usually bad. Every disc you own is a disc your opponent might flip, so strong play minimises your own count while maximising mobility — the number of legal moves available. Corners are permanent because nothing can flank them, and the squares adjacent to corners are the worst on the board for exactly that reason.