Do you mean that quests should be failable? A failed quest isn't broken as such, it's performed to specification. A broken quest is one that ends in limbo, neither completed, failed nor pending. (At least in my mind.)
For Example: George's Murder [color:"red"]
(Spoiler alert!)[/color]
To complete you must:
- Discover George's body.
- Report to Mardenus.
- Find the vampire.
- Kill the vampire.
- Report to Mardenus.
You can fail if (hyperthetical for this purpose):
- Mardenus is killed.
- The Vampire escapes.
Unfortunately, the option to report to Mardenus the second time is not available if you do not provide George with the Dundure he requests. This is not a crucial part of the quest but ultimately prevents you from completing it. This is a broken quest. It will eventually fail when you hit the gong and the council is attacked, but you did all that you needed to to complete it but it was not acknowledged.