I have been told (by those much more qualified in psychology than myself) that I am a self-sabotaging perfectionist. What this means is that I would rather not attempt something and fail through inaction than to make an attempt and get it wrong. Part of why I have this mindset is how I was raised. The outcome is what matters, not the effort. If I received at good mark in school, I was asked by my parents why I didn't do it perfectly, made to focus on the mistakes I made instead of the accomplishments I had achieved. It probably doesn't help that I became a musician, where getting something almost all right is unacceptable. Perfection, or as near as possible to perfection, is expected.
Now, onto the matter at hand. Being a perfectionist means that when I actually attempt something, I put my all into it. I take huge pride in the things I do, especially the things I believe I do well. Teaching percussion is one of those things. Another is being able to help people physically with my knowledge of reflexology and massage (though I have a TON left to learn in those areas). An obvious one is my knowledge of tea. And a big one is my ability to organize and make things efficient. When someone belittles or attacks my efforts in one of these areas, it is a huge assault on my pride. These things are areas of my character that I believe are fairly core to my being, and having someone say that my efforts are poorly done or worthless cuts me to my core.
What makes each individual person unique is what they define as their core beliefs. You can always tell when someone is discussing something that is foundational to them. They are more energetic, more passionate. They have a look in their eyes that even the untrained can see. What you need to careful of is what you say to people before you understand what these beliefs are for them. Something this personal usually takes time to unearth, with some beliefs being closer to the surface than others. The danger is that you may offend someone by calling them down on something that they feel strongly about.
Be careful when you say something with sarcasm or with the intention of being a light joke. You never know when you might be spitting in the face of their god (literally or otherwise).
Toodles!