Choosing your career is one of the most important decisions you will make, yet you often hear people say that they are stuck in a career that an eighteen-year-old chose for them.  They are, of course, referring to themselves, when they were eighteen. 

They may say that, because of how different the careers they chose for themselves turned out to be from what they initially thought they would, but most likely they are expressing that they would have made a different choice, if they knew themselves then, the way they do now.