The "don't become too focused" debate

*sigh*
So I do have some idea of what it is I want to do when all is said and done with school. And that idea has changed as I have crossed things off my checklist which I found did not meet some of the criteria I know I want in my career as a physician and things have been added as I have discovered routes and options that I had no clue even existed. And I am sure the latter will probably still continue as I enter into rotations and see more options in medicine.
However, I was talking with someone the other day here at school about one of my newer interests and quite frankly probably one of my top prospects of consideration, and he told me I should not become too focused and eliminate things. Huh????
I do not think I am *that* focused, I simply know what I want and know what I am bad at.
For instance, I am a clutz. I swear I can trip up stairs, and I have in fact done so. Knowing this, I know surgery probably not a good career choice for me. Is it bad for me to say I know this is not me at this point in the game knowing that the field and what it requires is not ideal for me??
Also, is it bad to say no I do not want to do OB/GYN because I do not want to have to deal with the insane hours of call that are required because you can not control when someone goes into labor (as much as we may try). This does not fit with my idea of what I want for my family. Is it bad for me to eliminate this at this stage of the game because the demands of the career are not what fits in my lifestyle and my personality???
I guess it leaves me in this crux. I am trying to keep an open mind to new things that fit what I want, but at the same time I think when you do this as a non-trad you have to have some idea of what it is you want and where it is you want to go. Otherwise, how do we endure all of the exams, all of the sacrifices we make, all of the junk we put ourselves through as we reach this dream?? What makes it worth it if it is not for the light at the end of the tunnel?? Why sacrifice a weekend with our family to spend time with 30 cadavers if not for the knowledge of the fact that we are doing so in order to be able to do what we were meant to do and what we love to do? And to endure that torture (sorry for those that love anatomy, but it is definitely not me), why is it bad to keep in mind the goal we are working toward?
And even now, as I debate the whole do I or do I not take the USMLE debate, why is it bad to have some idea of what it is I want to do? Does this not help me make that decision based on availability and location of residency or fellowship programs? Does this not help me decide whether I want to put myself through the horrors of two major board exams, one of which I do not have to take, in order to be abel to have a career as what I want to do rather than settling for something less???
I guess it just comes down to one of those non-trad things that some people, despite their best intentions, do not truly understand.