What's Already "There?"

Why do you have to do what you ended up doing as a kid?  What if that's not what you wanted to do?  You're supposed to change throughout life, at least in this day and age.  People think we have a tendency to go way back.  Like it's stronger, a very early stage or possibly birth or in the womb.  I'm not sure what I was at conception, but we all evolve into something.