I have three main characters in my current novel. The protagonist has two besties. Simple enough. This wasn’t intentional but it turns out The Triangle is universal in all fiction and there are reasons why The Triangle works so well. Let’s say Harry met Sally and fell in love. The number of interactions that there could be would only be two. Harry’s relationship with Sally and Sally’s with Harry. Add an extra character say called George and now you have 6 possible interactions.
Harry + Sally
Sally + Harry
Harry + George
George + Harry
George + Sally
Sally + George
If you added another character you would have 12 possible interactions and quite likely a very intricate and complicated novel. Add a fifth character and the number of interactions goes to twenty. Of course you are probably not going to have every character interact and bump into each other but trying to keep track of so many characters would be difficult. This is why The Triangle is the perfect equilibrium. Not too little and not to much.
Some recent Triangles I have just seen:
Clueless: Cher + Bestie + Friend she wants to fix
Ghost: Psychic + Ghost + Wife
True Blood: Sookie + Bill + Eric
How many characters are in your book and do you plan on adding or cutting any?