Elves! Hermione and Ron! TREE RAPE! There is much to regret in great SF/F...

I agree that Hermoine and Ron should never have married.

Tolkien's problem with the word Elves is that people had preconceptions.

Yeah, Tyrion is not an acrobat:

2. George R.R. Martin: Tyrion's acrobatics in A Game of Thrones. When Tyrion visits Winterfell, he has a physical prowess we don't in the later books. The early Tyrion jumps from a high gate, somersaulting to the ground, and it's one of the few parts of his expansive books that Martin regrets. In a 2012 interview, Martin explained:

Ahm... Wait... What would I like to change? Well, I might like to change the scene where Tyrion Lannister is first introduced; the scene where Tyrion jumps from the top of a gate; it isn't possible. By then I had very few references about people of his condition and it was later when I came to know more extended details about his physical challenges. So that's one of the things I would change

Yeah, Rick Grimes should keep his hand.

4. Robert Kirkman: Cutting of Rick's hand in The Walking Dead comic. Okay, it's not exactly a regret, since Kirkman says he wouldn't go back and change it if he could, but he has said that, as cool a moment as it was, having the Governor cut off Rick's hand in the comics has become a bit of a pebble in his shoe. After all, now he has to figure out how Rick performs small tasks like buttoning his shirt or opening a can. Kirkman has admitted that he didn't think through the consequences of cutting off Rick's hand.

Kirkman has said that it's fine in the comics because it's a static medium, but he thinks the TV Rick should keep his hand.

Yeah, Douglas Adams should not have killed everyone.

6. Douglas Adams: Killing everyone off in Mostly Harmless. The fifth book in the Hitchhiker's Guide to the Galaxy series has a major downer ending when the major characters are brought to Earth just in time for the planet to be destroyed by the Vogons. Adams later decided this ending was far too depressing, the result of a bad year on his part, and announced that he had plans to undo it. In a 1988 interview with Matt Newsome, Adams said:

 People have said, quite rightly, that Mostly Harmless is a very bleak book. I would love to finish Hitchhiker on a slightly more upbeat note, so five seems to be a wrong kind of number; six is a better kind of number. 

Adams didn't get to finish that sixth book, so Eoin Colfer undid the Mostly Harmless ending in his own Hitchhiker's book, And Another Thing...

Yeah, Twin Peaks should not have revealed Laura Palmer's killer.

9. David Lynch and Mark Frost: Revealing Laura Palmer's killer in Twin Peaks. This is another decision that came not from the creators themselves, but in part because of network pressures. David Lynch actually didn't want to solve Laura Palmer's murder at all, leaving it as a thread throughout the entire series (though he did say that maybe they could reveal the murderer in the final episode). Mark Frost, however, felt they had an obligation to their audience to eventually solve the crime.

Eventually, they caved to network pressures to reveal the killer, but the show went off the rails for the writers without a similarly impactful moment in the second season. Lynch always maintained that solving the crime so early in the series was a mistake, and Frost eventually came around more to Lynch's line of thinking, saying decades later:

 I had to kind of forge a compromise [between Lynch and the network]. I'm not sure that David wasn't right. Maybe we shouldn't have solved the mystery. Let it drift on into the background and churn up more incidents as you went forward.