Watching football, whether at home or in person at a game, is more fun when using the #mondaynightfootball hashtag. Dressing up as the anime character Jessie from Pokemon practically requires an audience who can say, ‘Whow, how did you get the hair to stay that way?” Very few people would show up to a Star Trek convention with no one else there.
Fandom is inherently social. But our fellow fans do more than just make things interesting. In many situations, they make things possible.