An open file is normally needed in king attack
The following game is a typical one of the category: Both side castling and a closed center. So let`have a look at our starting position:
Here we have already the both-side castling on the board, but the center is not yet closed. The main issue in such kind of position is to open at least one file at the attacking side for the own heavy pieces. Without this it is very difficult to enter the "castle". On the other hand the task of the defender is to hinder, or at least to make difficult such a file opening.
So let´s see how it worked in the game:
So what would have happened after 9. ... gxf5? Don´t forget, you want to open as much files as possible on king side