Shy adolescents often devote themselves totally to a hobby to help distract them from the loneliness brought on by their shyness. Sometimes they are able to become friends with others who share their hobby. But if they lose interest in that hobby, their loneliness may be exacerbated. So developing an all-consuming hobby is not a successful strategy for overcoming adolescent loneliness.
The statement 'Some other strategy for overcoming adolescent loneliness is generally more successful than is developing an all-consuming hobby' is an assumption required by the argument.