I agree with your first sentence, but not your overall premise. We are all capable of a hell of lot, usually much, much more than we realize, but not everything. I think most of us, myself included, need to take more chances to try and learn new things and error on the side of trying. However, the wisdom to realize something is truly futile is not a bad thing, after all, we've all got finite time and resources.
Adults are usually impatient. They don't see results right away and give up, not realizing it takes time! Children however can go forever without giving up, and I believe that's one of the (many) reasons why it is easier to learn a skill as a child. Sometimes it is good to remind yourself of this when you want to learn something new or feel like giving up.
