Motivation and Fulfillment - Designing Games - page 210

For example, a fixed ratio schedule creates a dip in motivation just
after the player gets a reward. If the player can get 10 gold pieces on every
10 th defeated orc, his motivation will collapse right after the 10 th orc because
he knows he has nothing to look forward to for the next nine orcs. This is
where the player puts the game back on the shelf—a “shelf moment” in
design lingo.
We can avoid such shelf moments by superimposing several fixed
ratio schedules. Consider what happens when the player can get a dollar
for every 10 th chest, a diamond for every 10 th rock mined, and an arrow for
every 10 th goblin killed. By the time the player opens the 10 th chest, he's on
the ninth rock mined, so he wants to finish that to get the next diamond.
By the time he gets the diamond, he's on the ninth goblin killed. By the
time he kills the 10 th goblin to get the arrow, he's on the 17 th chest opened,
and so on. Whenever one schedule reaches a motivation gap, the others are
at their motivation peak. The player shifts focus back and forth between
activities, never missing a dopamine-driven beat.
So-called grinding RPGs are famous for this technique. The player is
never more than a few minutes from the next major loot drop, character
level, or crafting opportunity. Each time he acquires one reward, he discov-
ers another that is just a few minutes away. The end result is that the player
can't put the game down.
The same mechanism gives turn-based strategy games like
Civilization V their addictive quality. “One more turn syndrome” appears
in these games because there are so many superimposed reward sched-
ules that the player is never more than one or two turns away from getting
some reward. Next turn, that technology will finally be finished research-
ing. One turn after that, it's a new military unit. Then, it's a new structure,
then the expansion of a border, and so on. There might be 30 or more such
reinforcement schedules running at once; at least one of them is always
keeping motivation high.
The key to superimposing reward schedules is that the player must
not be allowed to concentrate his efforts on just one reward schedule. If
the player can effectively ignore all but one schedule, he can finish the
schedules one by one and get into a situation where every schedule is at the
maximum distance from the next reward. That's a massive shelf moment.
RPGs avoid this by constructing their world so that the player is constantly
presented with opportunities to kill goblins, open chests, and mine rocks
even when doing something else. And in a strategy game, players cannot
reasonably focus on just one research or production task to the exclusion