An easy way to create an attack is to first create a weakness. Another easy way to create an attack is to open some lines. However, when you create a weakness, wouldn't it be better to open some attacking lines to the enemy king while you're at
it? Logically it would double the strength of the attack, with weaknesses and lines everywhere, all leading to the enemy king. - Wikibooks
How does White create these opportunities ?
Play the game - click on Black's 21st move for the position