Who Are You
You are a person who is living on the edge of civilization, either by choice or by circumstances. You travel the black of space on the edges of systems -- the kind of black that can only be matched by the blackness inside the people you sometimes meet on the border planets -- spend too much time in the Black, and the Black gets into you.
You don’t survive in this kind of life unless you’re driven by deeper needs than normal folk. This goes beyond dilettante interests and hobbies. Your obsession is your filter for the world; what you live for, what defines your existence, what gives your life meaning. Pick carefully. You want something useful, but original. It should be something simple to express. "Toughness" is a good obsession. "Getting really strong so I can beat people up" is pointless detail. (If you want to begin without an obsession and find one later on, talk to the GM about your idea.)
Your obsession is critical. When your brain is idle, your obsession is what your thoughts generally drift to. Even when you're thinking of something else, you tend to tie it back to your obsession. Your obsession isn't necessarily a goal -- it's how you understand the world. Generally, everything you see in the behavior of others around you can be explained in terms of your obsession. If it can't... well, that person's probably some kind of crazy.
Write your obsession on the character sheet, along with a short summary of what it means to you. Here are some examples from characters in the Firefly ‘verse:
The events in your life can have a profound effect on your personality; somewhere out there is something that scares you silly, something that ticks you off, and something that inspires you to action.
These are the passions that rule your life. In a way, they’re the real foundation of all the "logical" and "rational" decisions you make as a human being -- they run deeper than reason and intellect, stronger than willpower or drugs -- when they come bubbling to the surface, you are at your most visceral... most human... most true to yourself. These are the hot buttons wired deep into your persona; to deny them is to deny yourself and your humanity.
Your passions cannot directly contradict your obsession (though one might hamper another): you are a coherent, relatively sane person.
When you’re in a situation that pushes one of your buttons, you can opt use one of your Passions to either flip-flop or reroll a failed roll during that situation -- what you can use that reroll or flip-flop for depends on what kind of Passion you're calling on.
If you try to use a passion for bogus reasons and the GM calls you on it, you don’t get to cut loose. Yet.