In any game, there are mechanics that the player must learn in order to successfully play.

The simplest and most immediate example of this is the user interface (UI). The range of mechanics may be from controlling the onscreen persona to managing inventory to controlling other units/characters in the game.

Another kind of mechanics is embedded in the gameplay. For example, learning a special jump in an action game, or learning how to best use skill points in a role-playing game. These are more subtle, but still represent things that the player has to become familiar with and master.

It is the game designer's task to present these mechanics in a way that will not overwhelm or bore the player. Simply including a manual and tutorial may not be enough, and is perhaps unneccesary if the designer puts enough thought into introducing each new mechanic in a layered fashion, each building on the last. This is the essence of what I mean by learning curve, and it's one example of why game design is an art and not a science.

The learning curve could be said to be a subset of pacing, but pacing as I mean it here refers more to the actual activity of gameplaying. As with the other aspects of balance, it has a few subtle uses.

Pacing is important in that it is what defines the highs and lows of the game, the "energy" of it. Said another way, some segments of any game will be frantic and some will be calm times of contemplation (for example, combat is typically more fast-paced than poring over solving a puzzle). How a designer mixes sections of gameplay between these two extremes is what pacing is all about, and what can be the difference between frustration and boredom. Too much action can wear the player out or become redundant, and too little activity will weaken or destroy the player's interest in the game.

While pacing applies to the energy of a game, it also applies to how fast the game unfolds. For example, the beginning of the game should reward the player fairly quickly to build and sustain interest. Middles should pull the player along with moderate rewards spaced out more so that they are hard to achieve, but not so hard that they are never achieved. And the endgame is the finale, where the biggest reward is sought, but where pacing is just as important in maintaining interest and avoiding boredom by offering too many rewards too easily.

Finding the right pace depends wholly on the kinds of game elements and how they interact, and pacing should be taken into account when these elements are being invented.

In most games, the player's power within the game will increase as a form of reward and challenge. Sometimes, as with role-playing games, this "character evolution" is a central part of the fun. Character evolution ties in closely with pacing and even the learning curve, since character improvements can give rise to new kinds of actions (mechanics).

How fast the player gains new powers or becomes stronger depends on the style of the designer but also is a strong influence on how difficult the player percieves the game to be. A game in which there's very little evolution might be considered to be difficult, but that depends on if the challenges facing the player become harder faster than the player evolves. This is why pacing and character evolution are so closely linked.

A designer should probably view character evolution just the same as pacing other gameplay elements, and maybe include a chart to map out the corresponding rises in power with the rise in challenge. As difficulty rises, the player should be given the right tools with which to overcome them, whether that means new maneuvers in an action game or new skills in a role-playing game. These increases in power are rewards, so they should be treated as such and used in place of other rewards (such as cutscenes or a higher score) where possible since they add more to the actual gameplay than a simple, short-term reward.

Balance is composed of at least three elements: learning curve, pacing, and character evolution. Learning to combine these facets into a singular whole is one part of the art of game design, and it does take practice. Playing other games, and altering them where possible, is a good way to practice without investing effort in creating a whole game. Once you begin to master the balance of gameplay, you will be well on your way to better game design. And being aware of the issues involved is part of that progression.