He wrote the book on this opening
James West is a Life Master from New Jersey (where I used to live also). Although he has for most of his carrer played the Sicilian Defense as black in response to 1. e4, he later switched to the Philidor Counter Gambit (PCG) (1.e4 e5 2. Nf3 d6 3. d4 f5). Mr. West became so enamored with this opening, that he wrote 2 (!) books on it. He also has a blog at http://jimwestonchess.blogspot.com/.
So when I was scheduled to play White against him in the 1996 NJ Open, I knew the PCG was a definite possibility. So what do you do? Do you play some opening that you don’t know just to avoid the PCG, or do you try to study up on it, against the guy who literally “wrote the book on it”? I looked in the Encyclopedia of Chess Openings (ECO) vol. C (1.e4 e5 openings) at the book store set up at the tournament. The main line was given up to move 14 and evaluated by famous GM Paul Keres as “slightly better for White”. Unfortunately, the book store did not have West’s book on hand, so I had only ECO to go on. I liked White’s position. It seemed like “my type” of position, so, as crazy as it sounds, I decided to plunge into the main line of an opening that my opponent had written a book on (and I had never played in my life!) and see what happens.
First, it's just a game, so there's no need to be "afraid" of playing a strong player, or playing an opening he knows well, or sacrificing a piece in that opening. If you get a position that you like and play reasonable moves, you should be confident that good things will happen. What if you fall into a prepared trap that you knew nothing about and lose? Well, now you know! And you were probably going to lose anyway, statistically speaking, given the rating difference.
Second, I went into the game thinking "I know how the game is going to go start, and he doesn't" (since I knew he would play the PCG main line, but he didn't know I knew at least 14 moves of it). Also, he might be shocked or disturbed by the temerity of my playing the main line of "his" opening. Doesn't he know I wrote a book on this? Has he read my book and discovered a flaw? Is this a trap?
Third, even a strong player can be surprised by an unexpected move and react poorly to it. Especially when they felt they had anticipated all possible moves and one they hadn't looked at gets played, it can make them uneasy--"His move isn't a blunder, yet I hadn't considered it. How did I miss that? Is it good? What should I do? I thought I had this all figured out. He's rated lower than me. Why hasn't he played any bad moves yet like he's supposed to?" Just keeping yourself in the game and not doing anything stupid can often make your opponent take some chances to try to tip the scales, but they sometimes tip in your favor!