Zylr Cue says, "Basically (Mosconi) told me that I needed to develope a 'KILLER INSTINCT'. It all speaks to attitude though don't you think?"
Yes, Willie did speak to attitude, but bloodlust is not the proper attitude for pool.
Willie did not tell you to develop a "killer instinct" in so many words, did he? I believe that you are misinterpreting his advice and his attitude.
Willie said,
"Good players make the tough shots, Great players make the easy ones too." I believe he meant that the difference between good and great players is that the latter focus their entire attention upon every shot, not just the tough ones.
The greats have achieved
satori, a permanent state of Enlightenment and Correct Thinking, and they remain there effortlessly. The merely "good" rise to that level of consciousness only occasionally, temporarily, and with difficulty.
The good players are like an infant who is still learning to walk: he struggles to stand upright, consciously; toddles a few steps (in Enlightenment); and then falls to all fours again. But eventually, he learns to walk all the time; he becomes a "great" walker who needn't think about how to stand upright and fall forward one foot after another.
Willie then said,
"If you're playing your grandmother a race to 50 (straight pool), beat her 50 to nothing." It would be an insult to that great man to infer that he was recommending ruthless cruelty towards the elderly! Willie was, by all accounts, the epitome of a gentleman. He would never set out to humiliate anyone's grandmother.
I believe Willie was advising you to play the same fully focused game no matter who your opponent is. If you are a great player who has achieved satori, then your consciousness is
always totally focused upon what you are doing in the present instant. When you are shooting, you are not thinking about your relationship to your opponent, or how she gave you sweets and Christmas presents when you were little. There is no guilt about beating your grandmother to divide your mind and cripple your game.
Your opponent is irrelevant while you are shooting. (Whether that's the best "attitude" is a debate raging elsewhere, I know. Zen Cueism inescapably leads one to conclude that it is.)
Zylr says,
"For Willie it was all business. Always serious as a heart attack when he had his cue in his hand." Again, I think you misinterpret Willie's solemnity and concentration when he had his cue in his hand.
Satori, which Willie achieved if anyone ever has, is a sacred, rapturous state of consciousness. It is not grim, cold, or ruthless, as the term "all business" implies. The Zen Cueist in satori is serene. He does not display ever-changing petty emotions such as frustration, embarassment, anger, or frivolity. This tranquil state of blissful openness and unification with the Universe should not be confused with the anal-retentive closed-mindedness of being "serious as a heart attack."
No "killer instinct" should ever be sought. In satori, one is conscious of one's connectedness to every other thing. It becomes impossible to desire to "kill" one's opponent, for that would be suicide.