Self-talk and mindfulness are only parts of the picture, and how you perform these is important as well. If you are serious, you will need to do the difficult and boring work of improving the mental side, which is not a quick fix. It's a continuous, detailed and long process. 'Golf Beneath the Surface' is the best book I've found so far, it's very practical.
It's difficult for a lot of people to even start this type of work, as there is a deep sense of fear / dread involved (in people that need it most) and no real accountability to anyone, so I think a lot of people will be stuck where they are without improvement in this area. I have made a few posts about the mental game previously, you can search for them to understand my position more if you like.
The other thing I honestly do not understand is why someone who is not a professional would be so consumed with his self image from losing and winning that he would get frustrated when chance incidents occur.
Because it's a mental aspect of that individual, it really has nothing to do with a specific activity. You call it "a form of entitled arrogance". I would say it is a defense mechanism - the image of a fake-self is created to protect against feelings of inferiority or general worthlessness. The fake-self image comes with the belief that his opponent is low-level and he is superior. When that image is shattered by defeat or failure, those old feelings have nowhere to hide. They are usually expressed with black & white value judgements, absolutist thinking, catastrophising etc.
It's seems to be rooted in the idea that failure is shameful and a reflection of self-worth, therefore you can't allow yourself to fail. A lot of kids grow up in this environment, and therefore many adults have this problem. I find it so very common. This is why you sometimes see people 'not trying' when playing against certain players. They can't really fail if they aren't trying.
When chance is involved, it's a bit harder to figure out. The individual can feel like they have worked so hard, yet it didn't make a difference, deserves success, if not it was all for nothing. Perhaps, even though it was because of chance, it is still felt as a failure, because the immediate need for validation is denied. So the feelings are still there.
