Would you think that someone is doubtful to be more "good" at other field besides his/her educational background?

Of course not! I believe that anyone could be an expert in any field as long as they love it and have strong ambition. Lemme tell you something, i graduated from the faculty of Applied Arts, interior decoration department. I worked in my field for a year but some circumstances pushed me to shift careers twice. I worked as customer service at VF UK for a while and learned a lot from it then shifted to teaching. I have been a teacher for2.5 years and I love it. I believe that I am a better English Instructor than I was as a graphic designer even though it is what i studied at college. It is not about your educational field, i believe it is more about your skills and where you want yourself to be.

To someone who has: Strong desire to know something different.

Sure NOT. A passionate hobby, sometimes bring fame than the "premium education" acquired. It is passion that is "HOPEFUL"; over a doubtful university degree....!!

Absolutely!  A person's field of expertise can also come from what they have learned from family & friends, life experience, hobbies, and other outside interests.