In 1986 the psychology professor James Pennebaker discovered something extraordinary, something which would inspire a generation of researchers to conduct several hundred studies. He asked students to spend 15 minutes writing about the biggest trauma of their lives or, if they hadn’t experienced a trauma, their most difficult time. They were told to let go and to include their deepest thoughts, even if they had never shared these thoughts before. Four days running they did the same thing. It wasn’t easy. Pennebaker told me that roughly one in 20 students would end up crying, but when asked whether they wanted to continue they always did. Meanwhile a control group spent the same number of sessions writing a description of something neutral such a tree or their dorm room.

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