You are deeply, almost inhumanly determined to succeed at all costs. You may re-roll one failed roll each session and then only to directly further the end(s) to which you are driven — this represents an incredibly steadfast reserve of physical and mental ability, exerted only in dire circumstances.
However, as a driven character, any circumstance where your goals are in jeopardy is dire, and you must do all you can to thwart such circumstances — you may never hold back. You are willing (though not necessarily eager) to sacrifice everything, including comrades, friends, and loved ones, to assure victory. Note that the this character may or may not be willing to sacrifice himself, depending on his individual goals — although sometimes, a sacrifice is not of the flesh, but of the soul… if you believe in the soul. Many Driven characters do not, nor do they believe in chance — you make your own luck, they would say.
While appropriate for a villain, this trump was designed with a hero in mind — a tragic hero. As such it requires a serious and skilled role-player, and the GM must be judicious about allowing its use.