White should simply have extended with 24 as shown in Figure 7, which makes the white stones stronger without helping the black stones get stronger, too. This is another important Go principle: often the best way to attack your opponent's stones is to make your own stones stronger. Beginners like to say "atari" and do it every chance they get. But it is often a bad idea. In this game, it just made the black stone stronger without helping the white stones at all, which is exactly the opposite of what White needed. White 24 in Figure 7 strengthens the white stones at the bottom and it attacks the lone black stone, too. Now if White could play atari at 25, the Black stone could not get away (try it and see), and so Black must defend it by playing a move like 25 just the same as in the actual game. But now White has only one side to worry about, and 26 is one good move which will prevent Black from capturing the white stones on that side. The marked black stones in the corner are as good as dead. (More advanced readers will no doubt notice that it would be better for Black to play 25 immediately above 24, but White can still capture the marked black stones.)