To Be Able to Be or Not (Is the Question)

Here's a recent question that's been on my mind:

Is personality a deciding factor in choosing a profession? (i.e. Can only certain kinds of people do some jobs)

I am operating under the definition of personality that Elmer Towns has presented, which says that personality is composed of:

• intellect (power to know)
• emotion (power to feel)
• will (power to choose)
• self-perception (awareness of one's separation from other selves)
• self-direction (ability to dream/plan)

While I like to think that everyone is able to do any job they put their mind to, I feel like there must be some jobs that some people can simply perform better than others.  For example, if I had tried my hardest could I be a professional baseball player like I once wanted to be when I was little or would it have never worked out because I'm the kind of person that lacks the discipline for a sports schedule.  But then again, maybe I could have developed those qualities as I went along. 

As I write this, I'm starting to think that this question is basically one of destiny and whether it's created or fixed, which may turn out to be a pointless question to ponder in this life.  I guess I'll be whatever it is that I end up being and figure out the specifics in the end. (this sounds strangely familiar...)