You are basically a naive writer. You don’t really know how much of the screenplay time each one of your character deserves in the story. And often, you tend to get so used to them that you don’t let them leave. You ignore all the signs and all the loop holes that they are creating in the story. Their character gradually influences you so much that you end up turning them into the central lead role. Slowly and eventually, this character goes on to own the story. They spread and glorify themselves to such an extent that they ruin the whole script. Your script.
You see the problem here? It’s supposed to be your story. You are the lead role. Not some guy that you picked up in the auditions. They can never understand the essence of the complete story that you have in your mind. The dramatics here and there, for a while might sound interesting and might keep you on the edge, but you can’t lose your tempo for it. So, when a character doesn’t fit your picture anymore, it’s time to cut them off. Kill them. You don’t have to feel sorry for it . You are the writer and your story demands it. Go on and be grateful to them for being a part of a pretty important chapter. But then, be done. The story must move on.