the killer instinct

I have a NM /CM as a chess coach he says I have improved allow since I have started but now I have come to a stand still where chess is concerned, I am not improving anymore he says I lack the killer instinct and I need to learn how to sac pawns for positional development but I don't like to do that......... I have a tournament coming up in two weeks to decide that national team...... I am a junior player but their is another jr. player who is a national master. my coach says I can beat him but I need some more work............. any advice?

Don't let your 'coach' impose his own preferred method-of-playing {chess}, on yourself!; Which sounds, like he's a 'hyper'-tactical player!

I play 'positionally' {as in a 'slower' build-up, myself}; And, many {former} 'Great players' do.. or did! .. Remember; Along with 'studying' the game, {in All of its phases}; You may've heard the quote: "Success, in Anything; Is, 99% perspiration, {meaning long hours spent, in 'practice'}; 'And, 1% inspiration".. {or imaging, your eventual, hoped-for goal}.

The following 'Rocky' {movie} excerpt; Even though it pertains to another sport; May assist you, in the latter {1%}, 'imaging' yourself, successful, goal!  0: .. Cheers ..

https://www.youtube.com/watch?v=NubH5BDOaD8

The "Killer Instinct" is not necessarily about being tactical or sacking pawns or anything else. It simply means doing what the situation requires when the opportunity arises. In other words, it's about seizing opportunities.

The first world champion Wilhelm Steinitz put it this way: "The player who has the advantage must attack, or risk losing the advantage."

How a chessplayer defines the word "attack" will be different depending on his/her personality and experience. I'd say that to attack simply means to pursue an advantage. Indeed, years of chess practice has shown that you only have the right to attack when you have something to attack, or if there is a weakness to attack. You must be positionally sound before you can conduct a successful attack. 

The "killer instinct" is not only about attack however; it is also about defense.  It is what we both admire and fear in a wounded tiger: he will not go down without a fight. The "killer instinct" in chess enables you to survive. Every world champion had it, and they all had various playing styles:

Capablanca version of it made him look for the simplest and cleanest way to execute his plans, so as not to let things slip out of his hands. Fischer's technique was without comparison - everyone knew that once you let him get an advantage, that was the end of it for you. Petrosian was the most "solid" world champion in many players' opinion, but when he saw the chance, he grabbed the opportunity to squeeze his opponents to death like a python. On the other hand, when he was down, he knew how to seize an opportunity the very moment that the opponent let him off the hook, and proudced masterpieces of defense because of his sense of survival.

By the term "killer instinct," an experienced chess coach usually means that quality by which you never let an opportunity pass you by; you seize them when they come, and you try to create them when the position or the situation says it is justified. By it you win your winning games, and salvage some of those where you are in trouble by taking your chances when they arise. In chess, the "killer instinct" enables you to survive.

D-u-h ?! .. A pic.. plus a quote, is worth a thousand of your words ?!