Alex Curelea’s Dev Log

UPDATE: Got a response from Blizzard! Click here to read it.

Lately I’ve been amusing myself by reading Charles Duhigg’s “The Power of Habit” and playing Diablo 3 (not simultaneously). Diablo 3’s launch was a clear success, with 6.3 million sales in the first week, but also came with the predictable chorus of “the old game was so much better!” complaints.  One section in “The Power of Habit” struck me as an amusingly on-topic explanation of why some of the complaints have a grain of truth to them.

Why Diablo 2 was addictive

“The Power of Habit” describes an experiment performed on a macaque monkey named Julio. Stop me if any of this sounds familiar.

Julio was placed in front of a computer screen showing some shapes, with a lever, and a reward in the form of a tube with blackberry juice. The book explains:

First, he saw a shape on the screen:

Over time, Julio learned that the appearance of the shape meant it was time to execute a routine. So he touched the lever:

As a result, Julio received a drop of blackberry juice.

That’s basic learning. The habit only emerges once Julio begins craving the juice when he sees the cue. Once that craving exists, Julio will act automatically. He’ll follow the habit:

This is how new habits are created: by putting together a cue, a routine, and a reward, and then cultivating a craving that drives the loop.

Julio’s brain activity is particularly illuminating:

Even more interesting, once the habit is formed the reward response happens before the reward is even delivered:

The parallel to Diablo 2 is obvious to anyone who’s ever played it: see monster on screen, kill monster, receive reward in the form of an item that makes your character stronger. Diablo 2’s brilliance was in how the rewards were designed and spaced out – just powerful and rare enough to be meaningful, just frequent enough to enforce the loop described above throughout the game.

Why Diablo 3 is less addictive

On the surface, Diablo 3 would seem to follow the same basic structure: see monster on screen, kill monster, receive reward in the form of an item. However, for a number of reasons – many of them having to do with the introduction of an Auction House – the rewards are designed to be much more rare, and much less satisfying.

Diablo 3’s cycle is actually very different. As strange as it might sound, the reward comes from playing the game itself, which is for the most part very well done. The characters and skills are interesting, combat is a blast in the two middle difficulty settings, and satisfaction comes from bashing and destroying your way through the game world, complete with loud noises and shaking screen. Eventually the game becomes more difficult, and the only way to progress without being frustrated is to open the Auction House, buy new equipment, and proceed to enjoy the game again as your character is now significantly stronger - until the next time you get stuck and have to buy more equipment.

A hypothetical “enjoyment graph” for Diablo 3 might look something like this (forgive my crude diagram):

While for Diablo 2, it might look more like this:

Diablo 3 has no real reward loop – there is only a frustration loop, which can be temporarily alleviated by using the Auction House. As the game progresses in the hardest difficulty (Inferno), the frustration part of the loop gets longer and longer, as upgrades become more and more difficult to buy.

“The Power of Habit” has something to say about this, too:

When the juice didn’t arrive or was late or diluted, Julio would get angry and make unhappy noises, or become mopey. And within Julio’s brain, Schultz watched a new pattern emerge: craving. When Julio anticipated juice but didn’t receive it, a neurological pattern associated with desire and frustration erupted inside his skull. When Julio saw the cue, he started anticipating a juice-fueled joy. But if the juice didn’t arrive, that joy became a craving that, if unsatisfied, drove Julio to anger or depression.
[…]
For those monkeys who hadn’t developed a strong habit, the distractions worked. They slid out of their chairs, left the room, and never looked back. They hadn’t learned to crave the juice. However, once a monkey had developed a habit […] the distractions held no allure. The animal would sit there, watching the monitor and pressing the lever, over and over again, regardless of the offer of food or the opportunity to go outside. The anticipation and sense of craving was so overwhelming that the monkeys stayed glued to their screens, the same way a gambler will play slots long after he’s lost his winnings.

Ouch. Hits a bit close to home, doesn’t it?

In the end, Blizzard is left with two groups of players:

• New players will not experience Diablo 2’s reward loop, and will not get hooked. They will enjoy the game, get to the end, and (for the most part) wonder what the big fuss was about, lose interest, and wander away.
• Old Diablo 2 players will be left frustrated, unsatisfied by the lack of in-game rewards they were craving, and become angry, depressed, and reduced to flinging poo on the Battle.net forums.

Out of necessity, Diablo 3’s reward system has to account for the Auction House. Because equipment is never destroyed, in-game rewards can never be too frequent or powerful or they will flood the Auction House, eventually trivializing game difficulty. There have been many solutions proposed (here is one particularly insightful discussion), but the reward system seems so intertwined with the Auction House that it’s difficult to see a radical change coming. Blizzard’s response over the next few patches will be very interesting to watch.