Black is threatening to destroy the eye with a or b. is a good shape, sometimes called the table shape, to defend against both threats.
unkx80: Sometimes good feeling is important in life and death situations. Often good feeling can help one in making the correct choices, such as in this diagram. But this feeling needs to be cultivated.
is easily captured. This position can occur with a different move order -
,
,
, and
.
Of course, if there were a stone (black or white) at a, this defence wouldn't work because would be atari.
Now, Black's attempts at falsifying the eye all fail.