Coincidences -- this doesn't really count, does it?

That is a really interesting idea for a story twist.

The question really is what is the difference between a cool twist and a clunky coincidence. It boils down to the care and effort that the writer has put into understanding how the twist can be believeable. The reader needs to feel that there is more to the twist than the writer putting it in because it was convenient.

In this case, you need to ask yourself a lot of questions about why the MC doesn't know the bully is the brother of his best friend. The hard part is making yourself answer the questions honestly in a way that gives you a story without any holes. It is OK not to have the answers right away -- but you need to come up with them for the sake of the story.

Has the MC been to his best friend's house? Why hasn't he seen the brother there?

Are the best friend and his brother in the same school? Why wouldn't the MC know them both?

There may be very good answers to these questions (and others). But they have to come across in the story as well-thought out in order to have the big reveal feel like a twist rather than a coincidence.

Good luck with the story. Sounds like a fun one.

Doesn't sound like too much of a coincidence to make me roll my eyes. Sounds like a great twist in fact!

Coincidences that add to the plot are more acceptable than a coincidence that resolves plot problems.

For example; "No, I am your father!" Is a coincidence, but serves to complicate the story. Thats great!

If you had your villain standing over your helpless hero with a gun, saying 'Ah, how I've waited for this day, Mr Bond!' and suddenly getting killed by a falling meteor, is also a coincidence, and a very, very unsatisifying one.

I was worrying about how far I could take coincidences, then I thought about Pulp Fiction.

Remember when Butch was driving through LA and he randomly ran into Marsellus for no reason at all? And then ran into him?

Yeah. If Tarantino can get away with that, we can get away with some pretty ridiculous coincidences.

It's all about plausibility, and also how you write it. If you just pull it out of a hat for convenience's sake, then it's unsatisfying and probably downright dumb. Sometimes it's just mathematically impossible: Out of a city of 15 millions, it just so happens that the girl you just met is your half-sister who spent 20 years in Australia? That's when I roll my eyes and say, "Yeah, right."

If you're going to do coincidence, you need to make it plausible and leave enough crumbs for the readers to say, "Ah, now I see. Clever!"

Strange coincidences do happen in real life, but life is often stranger than fiction. In fiction, you need to take care to not take your readers out of the story by saying, "This is ridiculous."

If you had your villain standing over your helpless hero with a gun, saying 'Ah, how I've waited for this day, Mr Bond!' and suddenly getting killed by a falling meteor, is also a coincidence, and a very, very unsatisifying one.

Click to expand...

Deus ex machina!

If you just pull it out of a hat for convenience's sake, then it's unsatisfying and probably downright dumb. Sometimes it's just mathematically impossible: Out of a city of 15 millions, it just so happens that the girl you just met is your half-sister who spent 20 years in Australia? That's when I roll my eyes and say, "Yeah, right."

Click to expand...

Charles Dickens!

Consider also that in today's mixed families, there are so many different permutations of relationships, and that kids do form and dissolve "best friendships" on a regular basis. Lots of people don't have lifelong best friends.

If you had a situation where the two brothers were only half brothers, with different last names, it is plausible that your protag wouldn't realize that Billy Smith and Joey Walker were half brothers. Especially if at school, the bully was known by a different name. (In my family, we all use our first names for academic and professional purposes, but in the family, we call each by our middle names. This is a long tradition in my family and creates a lot of confusion for outsiders, which may have been the original goal. It sure helps weed out telemarketers.)

Also if one brother spent a lot of time at his other parent's house, and the two kids hadn't been best friends for very long, it's possible the protag would never have seen the enemy brother at the friend's house.

Coincidences only really matter when they don't feel like they could really happen.

This just sounds like a fun twist rather than anything that would feel impossible, as said before.

The ones you have to worry about are the Darth Vader *evil voice* "Luke, I am your father!" moments. It was new at the time, so it worked then, but it won't work, ever, ever again.