There are books out there where the protagonist works his way through the plot solo, without friends to bump ideas or thoughts off of. Without close advisers to interact with. Without friends to support or even irritate him.
Those books tend to have a lot of internal dialogue or are man-against-nature stories of someone trying to survive while stranded out in a snowstorm or at sea.
But most books I’ve read have the protagonist paired with another character. And I think it definitely makes life easier for writers. Think of all the ways a friend can help us out:
Provide the main character with advice and insight. The protagonist needs someone to bounce a few ideas off of. I love sidekicks in mysteries—they keep the sleuth from having long internal monologues about who the killer is.
Take the plot on a different path. The friend could talk our character out of a potentially good or bad decision. He could create obstacles for our main character or help him meet his main goal.
Help the reader know what the main character is thinking or feeling about something. Maybe the friend actually analyzes the protagonist a little bit, providing us with some background depth. “I haven’t seen you this quiet since your mom’s death when we were in high school.”
Introduce conflict. Maybe this friend isn’t such a good influence. He’s been the protagonist’s friend since they were kids, but he’s been in and out of trouble his whole life. Maybe he drags our protagonist into his seamy underworld while our main character is trying to rescue him from it.
Help reveal backstory. Like the example where the character helps reveal insight into our character, the friend can also shine some light on other important, plot-related events in the protagonist’s life, through dialogue. We have to be careful not to make this an info dump and to work it in seamlessly.
Provide humor (to release tension), or a great subplot. Even thrillers can use a little comic relief every once in a while. When life starts getting really stressful and tense in our novels, a little well-timed humor can do a lot toward reducing it. Our protagonist’s friends can also provide us with an interesting subplot (extra points for tying the subplot into the main plot).
Do your protagonists have friends? What role do they play in your novel?