Living Your Cover:
The first thing you must do is give up your identity. You will be given a new one -- your cover. Think of it as a new persona, one that guards and conceals the real you underneath, so you can carry out your secret mission with no one suspecting who you really are. Your cover story is tailored to you and to your mission. It must fit both, like a glove.
Just like an actor on a stage, you must live your cover and maintain the fiction of your new identity for as long as you are on a mission -- from a few days to several years. You must become your cover, your legend, and remember every detail, so that even under hostile interrogation, you will stay in character. Your mission, and your very life, depends on convincing people that this fiction is fact.