Three quick, general points:
1) I kind of like what "?" posted. There are definitely some Introvert types that can extravert very well and vice versa. What might be a stretch for one type might be a piece of cake for another.
2) One of the big lessons of MBTI is that the MBTI itself tends to be perceived differently to some extent by different types. IOW, one personality type might see the MBTI as prescriptive, another might see it as informative, another might see it as transformative, etc. And each of those viewpoints might be seen as a reason to embrace MBTI or to fight it.
I tend to see MBTI as transformative. As an INFP I seek ways to improve myself, and MBTI gives me insight into how other functions and types work. So I tend to welcome the opportunity to try out new functions and operate outside my natural comfort zone as an INFP. (I'm not saying that all INFPs are like me; but I think there's a subgroup of INFPs like me.) And if I'm favorably disposed to trying out other functions, I'm probably going to try harder than some other types to make those other functions work for me. And that leads me to the next point:
3) If working outside one's natural functions is uncomfortable, it doesn't necessarily mean that it's not doable or harmful. It may just mean you weren't ready for it. Growth isn't something that happens overnight. Sometimes one needs to try a new function or environment out a few times before it starts to feel like a good fit. If at first you don't succeed...
I've hit this situation many times. I tried a new job or a new skill for a while, it was uncomfortable and a bad fit, so I gave it up. But I hate to admit defeat, and I mulled it over for a while (sometimes years) and then tried it again at a later date. With the extra preparation and experience, on the second (or third or fifth) time around it suddenly turned out to be a good fit and even a lot of fun. Mastery of a tough skill can be the best and most rewarding kind of fun.
So personally, I don't rule out anything. One of my favorite quotes is from the Roman playwright Lucretius: "I am human, and nothing human is alien to me." (Homo sum, humani nihil a me alienum puto.)
FL