It's to not Screw up...
I don't mind getting killed, but I mind missing shots I should make, or misjudging something that leads to my death.
It like playing Tennis. If someone plays better than me, I'm impressed and happy in defeat. If I double fault, and hit every return into the net, I'm all pissed off.
Same goes with flying. 
My own experience is that
100% of my "deaths" are due to my own misjudgements, mistakes, inability to take advantage of specific situations or lapses in situational awareness. In my opinion, this game boils down to mistake management i.e. the one who makes the least mistakes wins....period. Even when faced against an opponent with better skills (e.g. E management, gunnery, ACM, etc etc) and/or other tactical advantages (i.e. altitude, relative E states, plane performance, etc) it comes down to who makes the least mistakes.
This is not to say I don't appreciate or discount the skill of my opponent. Someone who has better skills tends to make less mistakes and thus wins more. I personally try to go into every fight thinking I can win and even against a better stick that there is always the chance they will make more mistakes. Sometimes it even turns out that way!
I also personally feel once a person realizes their own mistakes are to blame for losing it improves their attitude. That's not to say I've not sent a nastygram PM or whatnot in the past....I'm human and when emotions run hot they tend to override judgement and logic....but it certainly helps.
