Sometimes the story wants to go someplace that you don't want it to go--or goes somewhere you didn't foresee. For example, consider the following sentences I recently wrote in my novel not an hour ago--yes, it is finally moving again.
A familiar cry sounded nearby. "Maston! Are ye deaf? Tell the men to unload, and do it sharpish!"
An incredulous thought crossed Aron's mind. Captain Jaskin?
The barrel-chested man stormed into view, a man in tow. "Sir," the man was saying, "I could not find a solitary man willing to--"
"Tis yer job!" the captain growled. "Do it right, or ye'll find yerself out of work. Permanently!"
The captain abruptly changed course and crashed into Aron. "Sir!" Aron said quickly, surprised.
Captain Jaskin raised a bushy eyebrow. "Aye? Why, if tisn't the Paladain lad 'imself! Are ye looking for work again?" His normally frowning face took on a slightly more pleasant hue. "What brings ye to this..." He glanced around. "This...place?"
Aron bowed slightly. "It is good to see you again, Captain. I...well, it's a long story, sir."
The large man clapped Aron on the back. "Then ye can tell it to me in my quarters. Come!" He said it with such force that Aron didn't dare disobey...
The thought of Aron, my character, going to Captain Jaskin's quarters didn't cross my mind until it popped up. Sometimes characters are just so forceful that they force the story to go somewhere else. You see, I needed Jaskin to take Aron somewhere on his ship--but Aron had to ask at one time or another. Instead of asking then and there, the natural thing to do would be to go somewhere comfortable to talk--his quarters. If you can manage to make your character do the 'natural' thing--that is one step closer to a better character.
Tolkien, in a letter to someone (I haven't the slightest idea who--I'll find out in a moment), once wrote this;
"I met a lot of things on the way that astonished me. Tom Bombadil I knew already; but I had never been to Bree. Strider sitting in the corner at the inn was a shock, and I had no more idea who he was than had Frodo. The Mines of Moria had been a mere name; and of Lothlórien no word had reached my mortal ears till I came there. Far away I knew there were Horse-lords on the confines of an ancient Kingdom of Men, but the Fangorn Forest was an unforeseen adventure. I had never heard of the House of Eorl nor of the Stewards of Gondor. Most disquieting of all, Saruman had never been revealed to me, and I was as mystified as Frodo at Gandalf's failure to appear on September 22."
-J. R. R. Tolkien, in a letter to W. H. Auden, 7 June 1955
In a fantasy novel, there are many more 'unknowns' than there are 'knowns'. If one pops up along the way, don't bother trying to revise it. Stuff that comes out naturally is usually good for your novel. It shouldn't effect the overall plot too much. If something pops up that you had not foreseen, then evaluate it. If it is good, keep it! If not, don't be afraid to cut it.