It has to do with our psychological attachment to a team, and in the literature, it’s called 'fan identification.' So, [the common term is] 'BIRGing,' which means 'basking in reflected glory.' When the team is successful, we tend to associate that we’re part of the team as well, so that's why you hear 'We played great,' and that’s because of this high level of identification we have with the team that supports our own self-esteem. We associate the success of the team with our own success.
It really comes out of research in psychology [in the ‘90s], where people were studying team identification. For example, how strongly I identify with the Philadelphia Eagles. And what they found was that for some people, it’s part of their self-esteem. So when the Eagles do well, it makes me feel better about myself and it also is part of my membership in a group. Other people stand around and have this shared experience, and that relates to group membership and individual self-esteem. One of the ways we retain our strong connection to the team is by really connecting ourselves as closely as possible, so when the team does well, in some ways, we’re part of that accomplishment.