I read an article yesterday about how the idea we're taught from infancy that, "We can do anything" is a sham and sets us up for failure. The author pointed out that we need to recognize our limits. When we believe we can do anything and then we aren't able to do something, we feel as though we failed. In truth, our bodies simply may not have been capable of that task. So we need to re-examine that, "Can we fix it? Yes we can," idea.
There's nothing my kids can't do. I don't let them use the word "Can't." I've told the girls from the time they were about 2 that there's nothing they can't do with help. If they're having a difficult time with something, they are not allowed to say, "I can't do it." They are to ask for help.
I agree about being realistic in our expectations (although, sometimes, I think our expectations fall short of our capabilities). So after reading that article, there was a moment where I worried about my insistence that the kids not use the word, "Can't." I'm sticking with it, though because I've never told them they have no limits (although I try to encourage healthy well-rounded limits.). I just encourage them to ask for help rather than throwing up their hands and refusing to try.