You are completely taken by some form of goal that you need to achieve and you are driven to fulfill it. Whatever happens you are almost consumed by the will to fulfill this goal. The trait is used in situations where you are hindered from following the goal and should be core part of your character's personality. In some cases, the Keeper may call for a check with this trait if you are exposed to a situation where you can pursue the goal, but probably shouldn't.
-1: A lesser form of obsession such as being in love with the girl next door. You harass her daily for attention, and her parents have eventually decided to go after you. What the girl thinks of the attention is irrelevant. It's your insistent behaviour that is the important part of the trait.
-2: This is more serious, as the woman may now be the wife of a local goon or your wife has left you for another man, and you have a deep seated need to find him and beat him within an inch of his life.
-3: This obsession is bordering on madness. This could be something like vowing revenge upon a goon lord who murdered your family, or the CEO who had your company shut down and left you without a job.
-4: The obsession has reached full madness. The goal of your drive isn't even remotely grounded in reality. It is something like trying to put the entire world under your feet as its one, true ruler.