React - remove event listener with (componentWillUnmount())

in this challenge we have to add an event listener (keydown) in the componentDidMount() and then remove it in the componentWillUnmount() after that if i keep the enter button down i see a message on screen. So i added the event listener successfully , but i dont understand what i did there with the remove event listener, i mean, how is it removed and when? cause i can still press the enter key in my keyboard and the message still appear on my screen.