Maria Caliban wrote...
Because a good character is one with a strong, well-defined nature.
I think you need to be careful with statements like this.
For a start, how do you define a 'good' character? I think (I hope) that we're capable of appreciating that fictional contrivance is not the same thing as lived experience. But for all that theoretical complexity, the average person is about as interesting as a pair of shoes. The tedious and unthinking call for 'realism' is inherently self-defeating because it is never what people actually mean. Even the most grungy, kitchen sink of dramas is inherently hyperreal. An accurate mirror of lived experience would be excruciating.
The thing is that bad characters can have strong, well-defined natures. A strong, well-defined nature does not mean they will therefore be blessed with verisimilitude, have crackling dialogue or even be very interesting. A character with a strong, well-defined nature can be as dull as paint and twice as forgettable. Which, if that is what you're aiming for, is great. Only... not great.
And good characters can lack strong, well-defined natures. Some of them are good characters precisely because of this. Dostoyevsky's Raskolnikov is such a fascinating, compelling character because he is erratic, unpredictable and an inherently untrustworthy protagonist. Do I 'know' Raskolnikov by the end of the novel? No, I would argue that I don't. Does that matter? No, and in many ways that is even the point.
'Consistency' sounds such a simple thing to hang your hat on, but in truth it is overrated. I'm not consistent from one minute to the next (granted, I'm a bad example) and the most consistent feature of people taken on masse is inconsistency. For me, change invites repercussion which invites change. The woman who behaves the same at a tea party as she does when fleeing an errupting volcano is in some form of denial. Whether that be due to lava or tea I leave up to you.