U Turns and other Inconsistencies

There's a world of difference between a beautifully-crafted character behaving inconsistently and the inconsistency that comes when a character is thrown together without much attention to detail, creating the impression that they are rather less than the sum of their parts.  The first is considered and deliberate, the second merely careless (or expedient -- sometimes a hero or heroine performs extraordinary U-turns in order to serve the plot.  Not a good idea.  The plot should spring organically from the way your protagonist interacts with situations and events). This kind of sloppiness will have any potential reader hurling your manuscript across the room.

You might, however, make productive use of the consequences which occur when a well-rounded, clearly defined character suddenly goes off the rails and does something untypical. It can have tremendous shock value, which is always a bonus, and sometimes it can send the story shooting off in a new direction. It will certainly give rise to a number of questions which you as the writer will then have to answer, so it will provide you with mileage and momentum.

Try writing a story that hinges on the heroine / hero behaving inconsistently. You have to pull off quite a difficult balancing act, ensuring that it is both plausible and surprising.