So far with what I am writing I have several very long files on each Major Character and several Minor Characters but a lot of the things that I seem to want to write down would require knowledge of how the person would react to different situations. I started to do this because I did not want to get into a situation while I was developing the plot where one of the characters might react to or interact with the other characters in a way that seemed uncharacteristic for them--no pun intended. So that is the situation and my question is how do most people approach characterization and plot creation. Do you create a general plot from start to end then work on the characters and define their personalities from their interaction with other characters or do you imagine these people in your mind and try and see what they would do given the situation and let that determine the specifics of your plot? Are the characters completely defined from outward appearance to multidimensionality before you even begin on the plot specifics or only the Major Characters? Does this ever create a problem where it forces you to deviate from the plot or run the risk of losing believability?