The main line is to atari at first before making an eye at . Due to shortage of liberties, a White move at a would be self-atari.
If chooses to destroy this eye instead, then captures and lives. White loses points this way.
Black's failure to make the necessary atari would be a fatal mistake. Now White can play ...
puts up resistance. But after , Black only has one real eye.
Directly preventing White to atari at here is futile.