The primacy of king safety is inherent in the rules. If your king is not safe, he may become trapped, and that means you lose. At the same time, you cannot win if your opponent's king remains safe. You must do something to trap the enemy monarch in order to win. So this principle is double-edged. It gives you a hint of what to keep in mind at all times during a chess game.
The first part of the principle implies safety for your own king. So the question becomes, “How do I make my king safe?” At the start of the game, he is surrounded by a queen, a bishop, and three pawns. Your king is in no immediate danger there.
The trouble starts with the other part of the principle. You begin the game by getting your pieces ready for an assault on the enemy king. But to do that, at least some of your pieces and pawns must necessarily leave the side of your own king. When that happens, he is no longer as safe as he was at the start of the game.
One of the best ways to ensure king safety is to tuck your big guy in a corner by way of castling. With three pawns in front of him and a rook by his side, and often a knight or even a bishop in the vicinity as well, your king has a good chance of maintaining reasonable safety for some time.
Both kings are reasonably safe for the time being. It will be hard to storm such secure castles.
Later in the game, this fortress may be broken down and your king may have to leave. But as long as you make sure that doesn't occur until a number of pieces have been exchanged via capturing, you should be all right.
The king often comes out boldly later in the game. When the danger of checkmate is reduced because the enemy doesn't have many pieces (by then a number have been captured), you can use your king as an added attacking force. Just make sure the danger of checkmate is really significantly reduced!
The Other King
The other part of the first principle is the enemy king. You generally can't win the game if you can't checkmate him. But of course most opponents are going to be very annoying about not letting you near their royal leader.
Against a reasonably skilled opponent, you will not be able to put together a quick checkmating attack. So you have to build up your attack, using the other principles to gather your forces for the final blow.
Meanwhile, you have to keep in mind the final target as well as your own king's defense. It's a delicate balance, and you'll be confronted with it throughout any given game.
The Fastest Checkmate
Perhaps you are wondering what is the fastest checkmate. It is referred to as the Fool's Mate, and it takes a total of two moves! The fool plays White, and the game goes 1. f4 e6 2. g4 Qh4 checkmate.
White used his two moves to expose his king to the maximum, and Black checkmated him.
It takes a little longer for a fool to lose playing Black: 1. e4 e5 2. Qh5 Ke7 3. Qxe5 checkmate.
Black's king blocks his own pieces from participating.
Another fast checkmate is called Scholar's Mate: 1. e4 e5 2. Bc4 Nc6 3. Qh5 Nf6 4. Qxf7 checkmate.
The Black king cannot capture the White queen because that would expose him to check from the White bishop on c4.