Connect the shared weak point
A double atari needs one ingredient: two of your groups drawing their last liberties through the same empty point. The defence is to deny that point before the opponent can use it — connect through it, as here, or fill it so the shape goes solid. Learn to see the shared point rather than the two stones: weak shapes announce themselves as a crossroad neither group can live without. The punishment for ignoring it arrives one move later from two directions at once, and only one group can be saved. Black to play: make the two stones one.