Old sea captain's trick

Endgame mistake  

The old sea captain's trick is a term coined at SL, for this situation where Black mistakenly responds to with the counter hane of , expecting White to block at , then connect at .

Instead, White cuts back at , allowing Black to capture at , then ataris on top with .

If Black now connects at , a white move at a will seal the fate of all the black stones involved in the skirmish.

The only thing Black can do is cut back again at b, and a picnic ko is the result, which is favorable for White.

Correct move  

Instead, Black should extend at . Now, if White continues at a, Black can hane at b and stop White's intrusion.

Note that the marked White stone makes a difference:

Different conditions  

If is here, and White tries the old sea captain's trick, then captures through and White is put on the spot (White could choose another variation, leading to ko, but that remains unfavorable)