So, let's say you're watching a new cop show on this thing called "television," which is an archaic form of tivo or iTunes. And the show, episode after episode, delivers great writing, crisp characters, tense situations and gritty, urban drama you want to keep coming back for. Oh, and the gruff Captain is played by an animatronic kangaroo.
I figure that might have happened for one of two reasons. Either the creators had it in there from the beginning, "Our show, Guts and Pouches, will be different from all the others because the gruff Captain is played by an animatronic kangaroo." And they were really excited about that. Or when they were turning in drafts to the network, some producer there said, "You know what this really needs? An animatronic kangaroo." And they grumbled but they put it in.
Two ways it might have happened; three potential outcomes.
1. No one notices. No review ever mentions it.
2. It makes the show. The Washington Post says "It's a keeper if only because the gruff Captain is played by an animatronic kangaroo." The kangaroo gets his own discussions at Television without Pity.
3. It's a disaster. From the beginning, fans and critics wonder what the hell was going through the creators' minds. It drags the show down. Finally, the kangaroo is gone.
I use a tv show as an example because unlike other forms of art, currently, it's cumulative. You have to keep going back to it. With other artforms, you get one shot to get it right.
I am currently deep, almost done with, a project in which I fret that in many scenes, the gruff Captain is played by an animatronic kangaroo. No one forced me to put him there. I did it myself. But, given that this is not a tv series I'm writing (SPOILER: I'm not writing a TV series), I have one shot.