Is "the killer instinct" essential for good chess play?  I know I once had this especially in OTB chess, but it may be a quality that fades with time--i.e. the steely determination to win.  It may not be useful if we actually have sympathy or human feeling for our opponent.  Any others?

Of course.  The essense of winning a won game is squashing any counter play.  It's like immobilizing a wounded opponent before going in for the kill.  And while the position is still equal you push for your ideas as much as possible while ignoring your opponent's / trying to prove his moves were a mistake in some way.  And when you can't do that you set traps and pitfalls.

Don't know who to give credit for this (Time?) but this says it well:

"But chess has a third--and unique--characteristic that is particularly fatal. It is not just monomaniacal and abstract, but its arena is a playing field on which the other guy really is after you. The essence of the game is constant struggle against an adversary who, by whatever means of deception and disguise, is entirely, relentlessly, unfailingly dedicated to your destruction. It is only a board, but it is a field of dreams for paranoia."

Reuben Fine?  Lasker's "Chess For Money and Chess for Blood"?  Sounds kind of sick...

Charles Krauthammer is the source for Wafflemaster's quote, he was writing about Bobby Fischer.

So, Krauthammer writes inanely about chess, also.

How would you know?

killer Instinct is like our intuition; our experience which are worth calculating.

Um, you stated he was the source of the quote.

No. I don't have a "killer instinct". It's a phrase that only brings about images of animals killing other animals to me. Though some chess players, I've noticed, like to fantasize about their game being likened to war itself. I suppose this amuses them in a rather dark way.

[COMMENT DELETED] -- by me.  too silly.  lol

Darn! I missed the "too silly" comment

I was reading some comments on the Wikipedia article on the great Paul Keres.  One comment jumped out relative to this topic:

His rival Samuel Reshevsky, while paying tribute to Keres' talent, tried to pinpoint why Keres never became world champion, and also complimented his friendly personality. "Well, I believe that Keres failed in this respect because he lacked the killer instinct. He was too mild a person to give his all in order to defeat his opponents. He took everything, including his chess, philosophically. Keres is one of the nicest people that I have ever had the pleasure of meeting. With his friendly and sincere smile, he makes friends easily. He is goodnatured and kind. Yes, he loves chess, but being a human being is his first consideration. In addition to chess, Keres was interested in tennis, Ping-Pong, swimming, and bridge."http://en.wikipedia.org/wiki/Paul_Keres

There is a distinct difference between being a friendly, or good person, and wanting to destroy those you are playing against, regardless of the game.