In the real game, a situation like this happened in the corner. Black resigned here; the marked move in the problem was never played. This problem explores why.
(;AP[goproblems]AB[ac]AB[ab]AB[bb]AB[cb]AW[ad]AW[be]AW[ae]AW[cc]AW[bc]AW[cd]AW[ce]AW[db]AW[eb]AW[fb]AW[dc]AB[gb]AB[gc]AB[fc]AB[ec]AB[ib]AB[dd]AB[de]AB[cf]AB[bf]AB[af]AB[df]AB[da]TR[da]C[Black played the marked stone; White to live](;W[ba](;B[ca]C[CHOICE](;W[ea]C[Correct!RIGHT])(;W[fa];B[ga]C[Seki; White could've killed]))(;B[fa]C[CHOICE](;W[ca];B[aa](;W[ca]C[Correct!RIGHT])(;W[ea];B[bd]C[:(])(;W[ba];B[ca]))(;W[ea];B[bd]C[:(])(;W[aa];B[ca])))(;W[ca];B[ba](;W[fa]C[Seki; White could've killed])(;W[ea]C[Ko; White could've killed]))(;W[ea];B[ba]C[Ko; White could've killed])(;W[fa];B[ca](;W[ea];B[ga])(;W[ba];B[ga])(;W[aa];B[ga])(;W[ga];B[ha])))