Holocaust victim Anne Frank and the fictional character Bridget Jones both kept a secret diary to record their innermost thoughts and fears.
Now a leading literacy expert says the increased likelihood of girls expressing themselves in diary writing could explain why globally they are outperforming boys in reading and writing.
David Booth, of the University of Toronto, argues that boys' psyche during early development and puberty means they are more likely to seek out company, rather than be on their own and read.
He says books alone are no longer enough to satisfy the reading needs of boys, who increasingly need a diet of other reading matter. Computer game manuals, internet blogs and graphic comics should become accepted reading resources in school libraries, Dr Booth told a national boys' literacy conference organised by the Assembly government in Cardiff.
He told TES Cymru that Wales should become an international testing ground for new approaches to boys' literacy problems because the nation is small enough to undertake meaningful research.
In 2007, only 61 per cent of boys in Wales reached the expected level in English at the end of key stage 3, compared to 77 per cent of girls.
But Dr Booth said boys' literacy problems were not confined to Wales. The issue is baffling teachers worldwide.
"Literacy is a solitary activity and boys are not solitary people," he said. "The traditional stereotype of young girl keeping a diary and reading alone in her room is crucial. It's different from how boys work; they are more likely to interact as a group."
John Griffiths, the deputy minister for skills, announced at the conference a Pounds 500,000 investment for primary and secondary schools to buy extra literacy resources. The government also plans to launch its own comic, called Time Troopers.
But wider availability of comic books was not nearly enough, Dr Booth said. Boys also love reading graphic novels and online texts, he says, and many will read manuals for computer games.
"Literacy involves all texts - visual, print and sound - and the ability to make sense of them," he said. "But many boys haven't had a choice before and don't know how to choose which books to read."
Dr Booth is adamant there is no lack of suitable books for boys to read, especially at key stages 2 and 3. But he said it should be for individual teachers to decide what works for their classes and pupils.