The rug gets pulled out

[Bushwhacker]

A primary election candidate's press spokesman is the one at doing his job. At the beginning, he's an idealist and has faith in his man. But after some time, he finds out politics corruption is all over, and so, at the end, he's even better at what's doing.

Here is the sentence:

"By the end of the film, the rug gets pulled out, and he’s even better at his job than he was before.

Please, what's the meaning of the rug gets pulled out.

[SoothingDave]

If you are standing on a rug, and it suddenly is pulled out from under you, what would happen?

You would fall down. You would lose your footing.

It usually means to suddenly lose one's position or that ones pretenses change. I don't quite understand its use here.