What exactly is the impostor syndrome? And why should we pay attention to it, when immediate concerns, such as planning for the week when we already have tons to do, seem to take a higher priority?
If you don't think you can live up to other people's expectations then it makes sense you'd try to protect yourself by minimizing expectations. So you decide that it's better to play small than to risk humiliation. Plus, you get extra points for being modest -- especially if you're female.
Often high achieving women refuse to accept their intellectual abilities and demonstrated success, instead preferring to assign themselves the role of the impostor.