The talking of characters being flat and round had always baffled me, and truth be told, it still does to an extent.
But I learned something important from EM Forster’s book, Aspects of the Novel, there is one line that sums this up pretty well :
“A round character must be able to surprise us convincingly.”
There are two important parts in this sentence. The character should surprise us, as well as the surprise being done convincingly. You can’t try to make a character round by letting them surprise us with something that they have no motivation or reasoning to do. If your reader can’t believe that your character would do something like that, then your characters had not succeeded in becoming round. EM Forster calls these characters flat characters pretending to be round.
Now the question is this. How exactly to we build up our readers into believing the surprise when it comes?
Every event that a character experiences can change him. Subtle changes, or major changes. If you can somehow create a series of events that would change him in such a way that it is not unconvincing when the character surprises, then you have succeeded.
But when you think about it, isn’t that the wrong way around? Shouldn’t you follow your character and bombard him with events and watch as it changes him? Then find him later surprising you with something? Then you think back and find that all the events had led up to this one decision? That all the events had changed your character in such a way that this one decision is convincing?
I would think so.