Have you ever messed around with GNOME shortcuts and ended up with all of the shortcuts turned upside down? No? Well I have.
To reset all shortcuts to it’s default state you can use:
gsettings reset-recursively org.gnome.desktop.wm.keybindings
or if you wish to reset just one shortcut you can use:
gsettings reset org.gnome.desktop.wm.keybindings maximize
where maximize in this case is the name of the property you wish to reset (eg. show-desktop, switch-windows etc.).