I joked the other day that I was going to implant GPS trackers in my characters, because I had no idea which direction they were heading.
It can be nervewracking when they set off down a different path than the one I'd initially planned. They give me a jaunty wave and say, "Let us show you what we have in mind", and I try to be brave enough to let them do just that. I remind myself that characters are meant to have a life of their own, and if they didn't, they wouldn't interest writers, or readers.
A TV show I used to enjoy, called Endgame, was about a Russian chess master, Arkady Balagan, who is unable to leave the hotel where he lives because he saw his fiancé get killed right outside the hotel. The last time he was outdoors was when he ran to her exploding car, but it was too late to save her. He is attempting to solve the mystery of his fiancé's death, and each week he also solves a variety of other situations involving hotel guests.
I wasn't sure there would be anything beyond this premise, so I didn't anticipate the show would hold my interest. For example, Arkady walks around the hotel in his bare feet, often wearing lounging clothes of some kind, treating the place as if it is his home, because it is. At first it seems a bit contrived--because it is.
However, the actor brings his own special interpretation to that collection of quirks and personality traits. He manages to inhabit the character so that what was a gimmick at the beginning actually becomes an indelible part of Arkady's persona.
It didn't take long before I was convinced he was acting this way because it's the way he is.
One scene shows him getting off the elevator, walking into the hotel lobby with his bare toes held apart by cotton balls since he just got a pedicure. It fits his personality perfectly. He's arrogant, and abrasive, insistent on getting his way, even when he's in the wrong. Yet we know he's in emotional pain from his fiancé's violent death, and we sympathize because he is doing his best to handle it, even if it is imperfectly.
These are some of the reasons he's endeared himself to me, so I continued watching the show, just to see more of his character and what he would do. (Unfortunately the show was cancelled after one season, so after getting attached to all of the characters, I was forced to let them go.)
They reveal bits and pieces to me as I go along, showing me what they're feeling, and telling me what motivates them. Soon I can see them as fully-developed vibrant characters. I may have to revise that initial scene, but it's worth it, because it gives me a chance to watch them grow into their personalities.
They become people worth caring about, and it's my job to develop their story to fit who they really are. So while I may grumble about not knowing where they're headed, I'm actually having lots of fun chasing them around, following them while we both discover who they are.
Just don't let them know that.