Fans – short for fanatics – can range from occasional TV show watchers, to football season ticket holders who show up to games in full facepaint.
When social psychologists talk about fans, they're usually talking about people who are active participants in the culture and community surrounding their subject of interest.
We become fans for a lot of different reasons.
But one big part of fandom is feeling a strong connection with your favorite characters, celebrities, and athletes – their struggles feel personal.
Some psychologists have been trying to understand why it feels so personal by studying how people respond to literature.
There's some evidence that when reading fiction, we "lose ourselves" in the character's experiences – a phenomenon called experience-taking.
In 2012, one small study had a group of college students read stories and share their thoughts about themselves, and the characters in the story.
Students who generally weren't as focused on their own internal thoughts and experiences seemed to more easily step into the main character's shoes, especially if it was a first person narrative.
This is related to something called theory of mind: the fact that you can recognize that you and I are two different people with our own motivations and goals.
There are two main parts to this idea: There's cognitive theory of mind, which is understanding someone else's intentions and knowledge, and affective theory of mind, which is understanding someone's emotional state, basically empathy.
In a 2013 study with a couple hundred participants, scientists found that subjects who read literary fiction with complex characters – as opposed to pop fiction, with predictable characters, nonfiction, or nothing – scored higher in measures of affective theory of mind.
How does this relate to fandom?
Like I said, it makes things personal.
When you're reading about Harry, Ron and Hermione, you can step into their shoes, and empathize with their fears, triumphs, and friendship.
The Wizarding World isn't real, but it feels real – and that's important.
A study from 2015 involving a little over 2000 participants found a bunch of different motivations for engaging in so-called geek culture.
They found that people who are looking for a self-esteem boost, or who are narcissistic, seem to engage in geek culture to play out fantasies that aren't possible in real life – after all, you can't go smashing orcs around town, but you can in D&D.
But these participants don't just isolate themselves in fantasy worlds, they seem to contribute to the real world in some ways, too.
The study found that many fans participate in civic activism, like self-help and nationality-related groups, although they seem to be less involved in political activism.
Their research also supported what they called the Belongingness Hypothesis.
That's the idea that people use common media – like Star Wars – to build communities and increase their sense of belonging.
Another study surveying fantasy sports fans, anime fans, and furries, found a similar trend, and found that people in different fandoms might have slightly different reasons for being fans.
Their research found that people who were anime fans or furries were more likely to participate in their fandoms because it created a sense of belonging, which was less common in fantasy sports fans.
The anime and furry communities tend to be ridiculed by society in ways that fantasy sports aren't, so the researchers concluded that fandoms can be a place where uncommon interests can be celebrated and shared.
So fandoms can be great!
They're a space where you can be enthusiastic with a whole community of like-minded people.
But too much of any good thing can turn sour.
If you become too attached to the characters or community of a fandom, it can become harder for you to feel empathy for other groups, like other fandoms, or non-fans.
There's a lot of psychological evidence that we feel more empathy for people who are in our communities than for people who are from different communities.
And when it comes to competitive fandoms, like sports, there can be negative effects when things don't go our way.
Like, one 2013 study even found that football fans are more likely to make unhealthy food choices the day after their team lost a game.
Depending on the nature of your fanaticism, psychologists have found that being a sports fan can be good for life satisfaction and self-esteem – called a harmonious passion.
Or it can make you kind of miserable by fostering frustration or hatred of non-fans – called an obsessive passion.
So it's important to be able to step back and see your fandom as part of a larger whole, and not let these communities become your entire world.
Strong social networks and relationships are good for your health and mental well-being, and hobbies and interests are important, as long as they don't veer into unhealthy obsession.