Bonnie Garmus had been a successful advertising creative for decades when she started writing the worldwide bestseller Lessons in Chemistry. That day, Garmus says a surge of anger about sexism overrode the rejection she'd felt when her previous book "didn't go anywhere". "For other writers, you should always realise that when you are filled with passion or anger - whatever shape the passion takes - it might be a good time to write it down," she tells Susie Ferguson.