I know that one of the main concepts of music is that it is meant as a vehicle to express humanity and to express human emotions. And, it can be felt by a listener if the performer is "feeling the music" or not when they play.
However, I don't think it is what it seems. In my experience so far, the times where I actually felt something inside of me in a kind of powerful way when playing, it wasn't so much that I set out to feel something and then tried my darndest to express that through what I was playing. There is probably a place for that, depending on the level of experience (perhaps) the performer has with the art.
But, what I have experienced as actually feeling the music was more like a kind of resonation within me to whatever was/is happening outside of me. A few times I have played something in my meetings with my mentor where I had not necessarily set out to express a particular emotion, but rather a particular musical idea or sound, and suddenly I found myself having a kind of reaction to what I was doing. It was as though what I was playing resonated within me in a particular way that it in some cases did cause a strong emotional response, or touched anyway some pool within me that was already there, bringing it to my consciousness.
By accident I have sometimes touched upon this in improvisation, but I could never consciously figure out how to do it on demand. I don't know that I could/should expect that I will always feel this kind of resonation with what I am playing but, for me, learning more specifically about how to connect with the musical idea sure seems like a step in the right direction.
Also, there was one resonation recently that seemed to tap into a pool of anger. Yes, I have some anger (I'm working on it). But, that is not necessarily what the music is expressing in that spot, it's just what my reaction was. So, as far as expressing *my* emotions there, that is not really my goal. I want to express what the musical idea is, and that may resonate with me in a particular way (and perhaps in different ways at different times), and perhaps I can use that resonation in the moments of my playing, but I don't *think* the music is truly about whether or not an individual knows what anger feels like.