At the recommendation of a co-worker, I recently read Jesse Schell’s The Art of Game Design: A Book of Lenses.
Like most good writers, Schell is a master of synthesis. He elegantly weaves insights from a broad range of disciplines, including psychology, anthropology, economics, creative writing, filmmaking and of course the newest kid on the academic block: game design.
The Flow Channel, an elegant model for player (and user) interest
In chapter 9, “The Experience is in the Player’s Mind,” Schell introduces one of my favorite concepts in the book, which he borrows from psychologist Mihaly Czikszentmihalyi (pronounced CHEEK-sent-muh-HY-ee). Czikszentmihalyi is famous for defining something he calls “flow,” about which he has written several influential books.
If you’ve ever been so engrossed in a task that the world seems to fall away and you lose track of time entirely, you’ve experienced flow. Flow is the state of optimal experience, a rewarding balance of our skills and the challenges before us. It’s the enjoyable feeling of being deeply engaged in the moment, and it’s during moments of flow that our best work is produced, our greatest ideas expressed and our most admirable achievements accomplished.
Clearly, flow is a good thing. But finding and maintaing flow is tricky. That’s where the Flow Channel comes in. 
This diagram visualizes some of the variables that can dictate the degree to which we are “in flow.” The diagram posits that as skill levels increase, challenges that call upon those skills must increase in difficulty, too.
If something is too difficult for our skill level, it will produce anxiety (number 1 in the diagram). Conversely, if something is too easy, it will create boredom (number 2). In the context of games, says Schell, players are most engaged — and most content — if they follow a roller-coaster pattern through the Flow Channel (number 3).
It’s more fun, in other words, if challenges sometimes seem too difficult — until our rising skill level flattens the curve. The ensuing mastery is also fun as we dominate an opponent or breeze through a level. But before it becomes old hat, the challenge level must rise again.
Angry Birds vs Bad Piggies
Experience bears out the truth of this diagram. Most recently, I surprised myself by happily blasting through Angry Birds: Star Wars, one of the top ranked games on the iTunes App Store.
I devoured its many levels, often playing them over and over to achieve a particularly satisfying destruction of blocks and bad guys. So when an in-game prompt urged me to try Bad Piggies, also created by Rovio, I though, “Sure, why not?”
Two minutes later, I was playing. And ten minutes later, I quit.
What happened? In terms of the Flow Channel diagram, I had veered somewhere into the upper left quadrant, where the challenge of the game was very high, but my skills were very low.
The resulting frustration ushered me right out of the game.
Two kinds of actions
Schell offers an explanation for how this can happen.
One of the reasons Angry Birds is so fun is because there are many ways to “beat” a level. Sometimes, you can feel quite creative as you use a special character in some clever way, creating a Rube Goldberg of destruction with just a single bird hurled at the right place.
This is no accident. Schell makes a distinction between two kinds of actions in games: operative actions and resultant actions.
Operative actions are the basic options you have in a game, the rules of play. In terms of Angry Birds, you have a fairly limited set of operative actions: you must launch a bird from a slingshot in such a way that you destroy the enemy. Different birds have different “powers” (some explode mid-air, some can shoot lasers, etc.), but you don’t have any control over the order in which birds are queued up.
Operative actions are the “verbs” of a game. They are what you, the player, can do at any given moment. Resultant actions are more interesting. These are the strategies and creative solutions that players invent based on the operative actions available to them.
So in Angry Birds, you could launch a bird directly at an enemy, assuring its comical demise. Or you could launch that same bird at the base of a tower, causing it to topple onto not one but three enemies. Much more satisfying.
The strategic decisions of how to launch a particular bird are resultant actions. In terms of game design, getting a high number of resultant actions from a small pool of operative actions is ideal. It’s elegant.
Thinking back to the Flow Channel, resultant actions are the skills that you build up as challenges increase in difficulty. They are what allow you to gain a sense of mastery over a game. For a while. Until new, more difficult challenges arise.
Too many verbs
Interestingly, if you give players too many options, it can create too much emergence. Schell warns:
Be careful, though — adding too many operative actions, especially ones that don’t interact with each other well, can lead to a game that is bloated, confusing and inelegant.
Which brings me to Bad Piggies.
The object of the game is to build a vehicular contraption that will get a “bad piggy” through the level. Simple, right? Early in the game, I was overwhelmed with the options I had for building my contraptions.
Not only did the number of components increase — wheels, umbrellas, bottle rockets, springs — but their orientation was sometimes variable, too. Then I realized that the placement of my character within the contraption could change the center of gravity for the vehicle, which could have catastrophic impacts on how the vehicle moved.
The operative actions, in other words, were too many to count. I saw before me a turbid sea of possibilities, and instead of feeling enthralled, I felt overwhelmed.
Jettisoned into the upper left quadrant of the Flow Channel diagram, I lost interest in the game. Had the game more slowly, conscientiously introduced new components, perhaps I would have stuck around longer. This would have limited the number of resultant actions, keeping me more happily adrift within the flow channel.
Bonus video
For more on flow, get it straight from the source, Mihaly Csikszentmihalyi, in this TED video.