Vital point example

Vital point  

To White has yet to establish a base. Textbooks will tell you that a is the vital spot for Black to attack White, threatening b.

In an example of the proverb my opponent's vital spot is my vital spot, White may well play at a to make shape:

Making shape  

...and this is the book continuation.

Making shape  

fills the marked Ko

although this sequence appears more common at the top level. the sequence a,b,c,d follows.