This is, of course, an exaggeration, and requires some careful explanation. I will not be offended if you tell me that I cannot fly by flapping my arms. Nor will I be offended if you were to tell me that I could not run a marathon tomorrow, although I would probably be a little irritated for a few minutes. And at the end of a long period of training and preparation when I actually did run a marathon, I would most likely be mildly insufferable, assuming I remembered the earlier incident at all. (Which I probably wouldn't.)
"Should" is a different word than "can", of course. Questions as to whether I should believe in God or how I should treat others are usually questions that deserve discussion, and I will not be offended if someone comes to me with a legitimate interest in having that kind of discussion. Without that legitimate interest, you likely will offend me, and telling me what I should or should not do without so much as an explanation will provoke a similar response.
So now that I've explained the exceptions, what was I getting at in the first place? Given that I am a college student, and classes start tomorrow, I might as well draw on those experiences for my examples.
Back in my freshman year, I signed up for what was billed as a lecture class in the politics department. This was back when I thought I wanted to be a politics major, and the class offerings that semester were very slim, thus leading me to sign up for this class that I had little interest in merely to preserve my "politics" credit, so to speak. When I got there on the first day and realized that limited sign-ups had turned the class into a seminar (requiring much more active participation from all students, usually aimed at upper-class students) with an extended research paper, I knew I was in for it.
The problem was that from the beginning, the professor knew that too. Could I have gone to her and said "I want to give this a shot"...? Well, we can't know now. All I can say is that it was alternatively disheartening and irritating for me to talk to her saying "I don't know about this" and to have her reply, effectively, "you're absolutely right to be worried because you shouldn't be in my class at all." Needless to say, pretty much the first thing I did was go and drop the class.
That was with a class that I didn't want to take. I agreed with the professor and still found it incredibly disheartening. When it comes to a class that I do want to take, a task I want to complete successfully, a field in which I want to be skilled? Well then, we'll find out what I can and cannot do when I do it, or when I fail.
And if I want to do something, I don't usually plan to fail.