The first part of your character sentence “I am an adjective noun who verbs” is the descriptor. It’s the adjective part of the sentence. It’s the most general, easily encapsulated means of describing any character—Resilient, Cautious, Strong, and so on.
Choose one of the descriptors in this chapter for your character. You can pick any descriptor you wish regardless of your type or focus (if any). Descriptors offer a one-time package of characteristics, usually training in one skill and a boost to one of your stat Pools.
Your descriptor influences how your character reacts to each new situation and challenge. For instance, the differences between a Cautious Ranger and a Brash Ranger are considerable, as are the differences between a Charming Starpilot and a Skeptical Starpilot.
Your descriptor matters most when you’re a beginning character. The mechanical benefits that come from your descriptor will eventually be overshadowed by the growing importance of your type and focus (assuming you’re not playing a game strictly set in the real world). However, the influence of your descriptor will remain at least somewhat important throughout your character’s life.
As the campaign progresses, a player might want to switch the descriptor that she chose when creating her character. As with everything, switching descriptors should be worked out between the player and the GM. The best play experiences come from good communication. If the GM agrees to the change, it should occur because something happens in the game to change the character or because her focus changes due to a new opportunity that arose in the course of play. If you just want to change for the sake of variety or to become more powerful, the GM is unlikely to allow it and may ask you to make a new character instead.
Changing a descriptor is both easy and appropriate. For example, in the course of play, a Kind vector's sister is killed by an agent of the Betrayer. The vector swears vengeance, and this justifies changing his descriptor to Unforgiving. On the other hand, if the vector falls on hard times and tries to lose himself in alcohol or drugs, he could change his descriptor to Addicted.
If a switch occurs, the character loses his old descriptor and its benefits. That should be part of the story, too. A Kind vector is no longer concerned about being helpful to others—now he's focused almost entirely on he own vengeance or erasing the world with drugs.
There's no limitation on the number of times a character can change his descriptor. For example, if the vector finally gets satisfaction, maybe he goes back to being Kind—as long as it fits the story.