"Impostor syndrome": what it is and how to combat it

Have you been promoted to a higher, managerial position but, instead of pure joy, you feel uncomfortable? Are you not sure whether you are the right person and, despite your career successes, you are still worried that people will sooner or later recognise your incompetence? Do you feel like you are not supposed to be where you are? Then you are probably suffering from so-called "impostor syndrome". What exactly is this and how can you fight against it?