One of my favourite topics in the doctor who fandom is the Doctorification of companions and how it often leads to their endings.
The Doctor needs a companion, that is a fact.
They can’t travel alone, it’s twists them, they need someone to stop them, to steady them. That’s where the companions come in. The problem is the doctor is addicting the more time the companions spend with him the more they become him, they start acting more recklessly and overestimating their abilities and their capability to always survive, because ,hey if they doctor can leap straight into battle with nothing but his wits and a sonic screwdriver, so can they.
They start losing that part of their humanity that tells them to feel scared, to not just leap into battle as if they are invincible because they are not, They are human, they can die, they are not invincible and while they can get close they can never be exactly like him.
And the worst part is, I think he likes it, when they become more like him when he is just about to have someone who fully understands him because they are just like him but then he loses them.
They change themselves to the point that they are no longer, what he needs, a human companion to steady him because at the end of the day the doctor doesn’t need someone exactly like him, he needs someone to steady him and to stop him.
Donna said it best he needs someone to stop him and the second the doctorification hits its peak the companion is no longer that and can no longer serve their narrative purpose. the dynamic is bound to get toxic and codependant and it will cause their "deaths".
