The initial position of the King has two main weaknesses: it is exposed on the e-file once it's opened up and the f7 (or f2) square is vulnerable because it's only protection is the King.
In the case of the e-file, it has to be open, or in the attacker's power to open it and he should be able to post a Rook or Queen on the file. It's also usually necessary to be able to strengthen the pressure by doubling Rooks or adding the Queen. Additionally, it is usually necessary that any piece defending or blocking the e-file can be attacked and eliminated.
In the case of f7 (or f2) a sacrificial attack has to be followed up aggressively so as not to allow the opponent time to muster his defensive resources. On f7 (or f2) the King has lost its right to castle and is exposed plus the diagonal h5-e8 is often a weakness. Remember, these weaknesses must be quickly exploited because they are usually of a transitory nature.
The following game was played in the Qualifying "C" section which was won Fine while his opponent finished 4th. For complete details of the tournament see Chessgamesdotcom.
Reuben Fine was truly a great player and had not circumstances intervened, there's no doubt he had a real shot at the world championship, or at least playing a match for it. When asked his opinion of Fine, Reshevsky's reply was, "He was a fine player." Asked why Fine never won the US Championship, Reshevsky replied, "It was because I was playing." The only time Reshevsky wasn't playing, Arnold Denker played the tournament of his life and finished ahead of Fine!
His games show him to be a formidable player with a solid, sound style. He described his approach as one where his chief objective "was always precision, wherever that would take me.” Euwe wrote that when Fine needed to win, he didn’t “take risks in order to avoid the draw and seek critical positions … [instead] … he simply intensified the accuracy and mathematical rhythm of his positional play – and scored win after win with surprising persistence.”
Most of Fine's wins were the result of his positional understanding and technical ability. This style doesn't have a lot of appeal to those who love swashbuckling chess, but it was effective and instructive.
In addition to his comprehensive book on openings, two of his most famous books were The Middlegame in Chess in which he explained the basic elements of combinations and attacks against the King, but mostly discussed how to evaluate a position, how to handle superior, equal, and inferior positions, the significance of pawn structure and space and the transition from opening to middlegame and middlegame to endgame. The other was his classic Basic Chess Endings published in 1941. It is considered the first systematic book in English on the endgame. CJS Purdy described it as a monumental work, one of the most complete and authoritative on endgames in any language.
In the following little known Fine game we see him execute an attack against the King after black delays castling one move too long and gets it stuck in the center.