John - now being treated for social anxiety disorder - used to struggle to get out of his apartment to eat.
He eased his fears by eating lunch at the same fast food restaurant, terrified of making mistakes if he tried to order food in other stores.
John was among about 10 patients recently diagnosed with the disorder at the Chinese University's mood disorders centre.
In his early 20s, John said he used to miss more than 100 school days a year because he was afraid of sitting in class with other students and teachers. 'They seemed to stare at me all the time and that made me very nervous. So I always found excuses to skip classes and stayed alone at home,' he said.
John said he developed SAD at 14 after being criticised by his classmates over a public speech. And fear of talking to strangers made job-hunting difficult. However, after treatment at the centre in March, John felt confident about finding a job.
His clinical psychologist, Kathleen Kwok Pik-san, said: 'During the treatment, I gave John a long shopping list. He learned to have conversations with cashiers and that helped him to overcome his fear of contacting strangers.'