Imposter syndrome is a pattern of inner thinking that your success is by chance rather than through your skill, competence or experience. It leads to self-doubt and crises of confidence.
Thousands of high achievers experience the imposter syndrome. They have a loud inner critic. And presume that 'luck' has got them where they are today. They fear being found out.
You probably wouldn't know as they have learned to cover up. They pretend and act as if everything is OK. Their outside life looks perfect, yet inside, they are doubting, criticising and questioning themselves.
This doesn't mean they are quivering in a corner and not leaving the house. It is often the opposite. They are leading teams to successes, delivering inspiring speeches, commanding high salaries and winning awards. All whilst doubting themselves and worrying about what others think.