What made Fischer so fascinating
Bobby Fischer was completely unpredicatable and totally inaccessible. The logic behind his actions was understood by no one except himself. Chess was all his world was about, and to his thinking, the Russians were dominating the brain game unfairly and unscrupulously, to propogate the superiority of their Red ideology.
He was an extremely strong player always, but he suddenly became invincible during the games leading to his winning the chess crown in 1972. In earlier years, he had been dominated at the board occassionally, in particular by Tal and Spassky, the latter as recently as 1970, but he now became virtually unbeatable, starting with the last third of the interzonals, through the candidates, upto the last and clinching game in the world championship.
His style was simple and to the point, but he could play complex and long winded games if required, against the brick wall like defences of masters of the draw like Petrosian, and win. Larsen said that Fischer was nervous during the world championship match against Spassky, but that at the board, he had full control of himself. Grandmaster C.H.O'D Alexander put it elegantly, saying that the tall, awkward and spotty Fischer suddenly relaxed as he sat at the chess table, and became almost graceful as he handled the chess pieces. (It is fascinating to watch Fischer setting the pieces on the board - there is a clip on the internet showing him doing this.)
Fischer had a long history of refusing to play major tournaments, mainly on the grouse that the Russians were giving their favoured colleagues easy draws while playing their best against outsiders. The Fischer Spassky match was nearly abandoned and only rescued at the very last minute.
He was not one to chit-chat with his Soviet opponents, usually giving them a wide berth during the games with them. It is said that he went for a win in every game, and usually annihilated even slightly weaker players. Another quirk was that he always opened with PK4 as white (e4); the fact that he varied to the queen pawn opening for several games in his world championship match does show a grudging respect for Spassky.
At the board Fischer was said to have an aura, which affected his opponents. Somehow, none of them were at their best against him during this time. Part of this could perhaps be attributed to the almost disconcerting speed with which he played his moves; he invariably had more time on the clock than his opponent. Almost all who played him on his path to the world title, Taimnov, Larsen, Petrosian and Spassky, seemed to have permanently lost their poise at the board and never figured seriously in chess headlines again.
With regard to Karpov, it was reported at the time that Fischer was watching the machine-like Russian's games closely, (through binoculars; to read his expressions?) but that is not to say that he must have feared him. We know now that Karpov had psychological vulnerabilities which were on display in his 1984-85 world title match against Kasparov: needing to win 6 games, and leading 5-0, incredibly, he couldn't clinch it, and the match dragged on and on and was ultimately abandoned after 48 games, with Kasparov having narrowed the gap to 5-3, and Karpov near breaking point. In a previous world championship also he struggled to win by a whisker against the flamboyant Korchnoi.
As to the possible outcome had their encounter happened, while Fischer was not known to spare the slightest weakness in an opponent's make-up, the fact is that it was he who refused to play, and therefore the benefit of doubt should go to Karpov. But this is far from the case, and many chess players are convinced that Fischer would have prevailed.
The truth appears to be that having made the breaking of the Soviet monopoly his life's sole objective, achieving this goal must have left him empty of the driving force which had led to his superhuman performances at the board. He now had to defend his world title, but defence was against his grain, de-motivating. He had crushed all his opponents, there was no one left to crush. He must have decided that even if Karpov was beatable, crushing him was out of the question. Without these powerful motivations, Fischer may have felt vulnerable, and after carefully weighing the pros and cons, and recognizing that nobody, including himself, could improve on his record in the previous world championship, decided that the best course was to leave an unsurpassable,if controversial legacy.