How does the "shrinking circle" quick time event work?

I just started playing the new Tomb Raider game and like a lot of modern games, it insists on those irritating press-the-right-button-at-the-right-moment minigames or quick time events to get your character through a sticky situation.

One of these is a shrinking circle where apparently you're supposed to press something at a specific moment, but no matter what you do it just doesn't want to work.

Does anyone know you're supposed to win this?