I threaten to take out the pawn on c7 with my knight, which would be a fork of my opponent's King and his queen's rook. This is a move all but probably the least experienced of chess players rapidly become VERY familiar with.
Is it worth bothering with in this game? My opponent castles rather than risk trying to find out ...
... whereupon, though it would probably have been wiser to have protected my h-file rook with my queen, I attack his King with my knight anyway, albeit in his new castled position. He runs to the ALMOST clear h-file, happily ...
... and I help him clear the rest of it, INCLUDING my king's rook ...
... a task he only reluctantly helps me with ...
... because he can see exactly what sort of prison my queen and knight have MADE of his castle, thanks to said cleared h-file. It's the chess equivalent of a Game of Thrones sky cell. Welcome to the Eyrie, friend.