Why does author consider the characters motivations?

When the writer knows a character's motivations, she can write actions that make sense for that character in a specific situation. ... Knowledge of character motivation—knowledge of who the character is and why he is that way—helps the writer add layers and depth, veracity and cohesion, to story. It gives truth to fiction

through negative experiences we learn many things its sort of like karma if u do something bad to someone and u get a consequence u dont like the next time u wont do it again and as for positive ur not really learning anything and another example for negativity people didnt want barrack obama as president because they thought he was the worst and he was taking but now we have donald trump   and hes   is not anyone and shut down the government over sum petty stuff unlike barrack obama who shut down the government because they did not want to give health care to the community and now these people who want him out want him in now