A recent article by IM Silman at chess.com, "The Difficult Opponent", provides some useful insight into what makes particular individuals - of similar strength or even below that of a player - become someone else's chess nemesis. Silman never actually uses the word "nemesis", but many of us have experienced the phenomenon where it seems that every time you play a certain opponent, they "have your number".
The article focuses on the idea of a matchup in chess style between two players that significantly favors one side, rather than emphasizing the psychological factors between the two players, although Silman also gives that some credit. However, although he provides some entertaining examples, he never really defines what aspects of the chessplayers' styles contributed to this.
By comparison, the factors that go into personal pluses or minuses against particular opponents were also discussed by Viktor Kortchnoi in his "My Life for Chess" DVD interviews. There he talked about his record against various top players during different phases of his career, which sometimes had more to do with playing strength and preparation, while other times it seemed more due to psychological dynamics.
To gain additional personal insight into this, I examined one series of games played during the later portion of my scholastic career against an opponent with whom I always had significantly more trouble than others. In two out of three games I nevertheless managed an undeserved result (win or draw). He had a somewhat unusual style, content to exchange off and head for endgames, which he understood better. This matched up in an asymmetrical way with my understanding of endgames (nearly nonexistent) and the transition from middlegame to endgame. My opening selection was also conducive to his style, as I had White in all three games and played an unambitious line in the English against his Queen's Indian setup. What I think threw him off in the end was my refusal to give up (tenacity) and my ability (with some luck) to find unexpected tactical resources. One could even say that we were "difficult opponents" for each other, for different reasons.
Another more recent example for me has been a two-game tournament losing streak against a lower-rated opponent. Both games I should have won and I was looking forward to the second one as a revenge opportunity (which never materialized). I hope the third time in fact, will be the charm.
Which brings us back around to the psychological factors. I analyzed both of the games (the first being Annotated Game #116) and the common feature in both was that I made things more complicated for myself - and simpler for the opponent - than they needed to be. Part of the challenge in my next game with this opponent, if and when it occurs, will be making the necessary correction in my approach to the game, along with not getting psyched out by our previous history. I think the latter consideration starts to loom large in a player's thoughts after a losing streak gets going, so can become a perpetuation of defeatism. One way to break out of the mental trap - I believe probably the best one - is to focus on playing the board, not the opponent. This requires mental toughness but is quite doable, unless your opponent is truly significantly stronger than you are.