You are what you do.

Karma, to a Buddhist, is not fate; rather, it is an energy shaped through conscious thoughts, words, and actions.

The common understanding is that your karma has been determined by something you did in a past life or earlier in this life; karma is viewed as a cosmic justice system. But in Buddhism, karma is an intentional action; we create karma every moment, and the karma from the past, and the present, effects us every moment we live (this is a key point: your past and present actions affect the present, and your present actions affect the present and the future). Your actions are karma; and your future is not set, but can be altered by changing your willful acts and self-destructive behavioral patterns (e.g.: Ebenezer Scrooge in Charles Dickens’ A Christmas Carol). Karma is the action, not the result: the results of your conscious actions are the fruits of karma.