I was having a discussion with a talented co-writer, Mark Lewis, about sitcoms and Dr Who last week. We began by discussing the common format of having sitcoms based on 3s: Will and Grace, Frasier, Only Fools and Horses, Father Ted. It was interesting to think about how this works. We considered the potential for conflict, variety and what the represent.
With just two people you have a single axis for conflict. With three people, this is tripled. You have the opportunity for 2 v 1s. In addition, it retains the benefit of 1 v 1. A common writing trick for generating conflict between three people is to consider them as an adult, child and parent. Now, they don't have to be those in reality or all of the time. They just need to behave that way during the scene. I began to think about what other trios you could have. Here are some ideas:

We wondered also whether pairs or threes work better when on the move. So threes such as Preacher and On the Road. When in a two, you tend to stay together as its dangerous. So, in terms of the hero and his companion. Often the companion does run off and get in trouble or find something useful. Threes offer the opportunity for two hiding something from the other.
Now, Dr Who. Is it a two or a three. Well, it seems like a pair. the Doctor and his companion. But might the Tardis be the third. Or K9. Not really, as they don't have enough human-like qualities to generate sufficient and sustained conflict. Interestingly, in the recent series of Dr Who, it has become a three as Nardole is a regular. So if this is now a three, does it fit the adult-parent-child template? Perhaps:
Dr Who = Parent (rules, sensible, stopping accidents)
Assistant = Adult (grown up kid, mature but irresponsible)
Nardole = Child (gets in trouble, silly)
If the companion is an assistant, they'd help the Doctor to be fulfill all three. So while the Doctor is being two of the three, the assistant can be the other. So if they are childlike, they will need to be saved. But it was pointed out that the Doctor can be all three, sometimes at the same time (episode). He can be naive and be childlike - custard and fishfingers - so why does this not work? Perhaps, its because he's an alien. He can then show us all elements of human existence. The best and the worst. Just like a hero. But more than a hero since he has 'superpowers' - a time travelling spaceship, sonic screwdriver and high intellect. So a superhero has the character traits of a parent, assistant and child.
Does this ring true? I think in the Marvel universe, it does. There is humour, often childish. They are parent-like in the sense of protecting 'ordinary' citizens. But they are also adult like, being selfish and deceitful. I think the DC universe is more focussed on superheroes being adults and parents. There is little humour in their movies. Even in something like Suicide Squad, its an ironic or sarcastic version of humour. Perhaps the fact that rarely a 'human' dies in DC relates to it also being more parent like - protecting the child (citizen) from the world's realities. Perhaps the lack of the child in the DC trilemma, has pushed everything to the adult and parent axis - creating a more leaden experience. So why did Wonder Woman work better? In a small part, I think it was the child like moments - eating an icecream, wanting to see a baby. All very childlike moments.