If you are ever overcome by feelings of self-doubt, just remember Agatha Christie. In April 1958, her play The Mousetrap became the longest-running production in British theatre, having given 2,239 performances to date. Her producer had arranged a party at the Savoy Hotel to celebrate her success.

She donned her best bottle-green chiffon dress and elbow-length white gloves, and made her way through the lobby to the party room – only to find that the doorman failed to recognise her and refused entry. Instead of hastily demanding “Don’t you know who I am?”, the 67-year-old author meekly turned away, sitting in the lounge all by herself. Despite outselling every other writer of the time, she said she was still paralysed by “miserable, horrible, inevitable shyness”.

“I still have that overlag of feeling that I am pretending to be an author,” she later wrote.

How could someone so successful still be so insecure? This is the paradox at the heart of a new book, Shrinking Violets, by the cultural historian Joe Moran, which explores shyness in politics, literature and psychology. Shyness may seem a trivial matter to those who aren’t afflicted, but as Moran points out, these feelings can even be a matter of life and death; the American doctor Henry Heimlich (who gave his name to the Heimlich Manoeuvre) once observed that “sometimes, a victim of choking becomes embarrassed by his predicament and succeeds in getting up and leaving the eating area unnoticed. In a nearby room, he loses consciousness, and if unattended, he will die or suffer permanent brain damage.”

Interested to know more, I called Moran to discuss the inspiration for his book and the conclusions he has drawn from his extensive research.