October 30, 2013 11:29 AM EDT
No particular reason needed. In a world and with a lifestyle that forces our characters to kill, maim, pillage and scavenge for a living, being evil is simply a step down from the dais of fairy tales and good knights and a step in a worldview that is based on pragmatism, to reevaluate what are the priorities of our character and more important of all the road they are about to partake.
All in all our character is a hero, this does not mean that he has to look for others and save kitties but the first and foremost need is to survive. Being a Dragonborn, or if not a guild master, a person of renown, attracts many people who want to use our power for their own benefit and it attracts enemies who are jealous of our power, and in a world rife with mysticism who know what boons could the daedra or the aedra bestow upon one who has defeated such a figure of legend such as our characters.
In the end your character should realize that she is being used and she will continue to be used and abused until she would make a stand for herself. This means that she decided to keep her precious soul and the power all for herself and to not be used anymore she would begin to hoard power, spells, magic items, everything that would give her the edge and allow her to prosper and survive.
It is not evil per se, it is self preservation. Once you learn that you are Dragonborn, immediately you are plunged into a world of enemies and interests that revolve around you, it is a choice to either serve the others or serve yourself, and your character simply decided that a good death of old age is preferable to a heroic one fighting a deadly foe on the behalf of the Nord people and their lazy Jarls, who first and foremost see in you an useful asset to further their agendas. Thus evil, but not evil as we intend, but simply egoistical.
Than from here on, the lure of power, the things you can achieve by using others to do your biding, the power that your dragon soul entitles you to, all this is intoxicating and before you can notice it you are an avatar of purpose and iron will, a monster who has become a monster in order to fight monsters, a creature that understands its divine origin, its top position in the society and than you shed your mortal flesh and you become a Dov, in mind, in blood and in soul.