If you call what you do a “job,” then you are probably unhappy with what you do. You go in for your required hours, collect your bi-weekly paycheck, and hope things will get better one day.
If you call what you do a “career,” then you probably have a job in which you are a bit more happy (at least ostensibly). You probably make a decent salary, have decent benefits, and there’s probably some opportunity for advancement if you work obsessively hard. The sad truth here is if you are this person, then you are the least likely to change, and thus you are the least likely to find your mission: you feel comfortable, which means you feel satisfied enough to keep on trucking, and maybe “some day” before you die you will be able to retire and live a more meaningful, enjoyable life.
If you call what you do your “mission,” then good for you—that’s outstanding news! If you’re living your mission, it’s easy to see you’re happy with what you’re pursuing: you have a sense of meaning in what you do, and you feel fulfilled and free because you are on a mission—you are doing what you were meant to do and enjoying it.
If you have a job you hate, it’s easy to change—you just need enough leverage. Usually the easiest way to find leverage is to discover your mission.