Cognition: Mental Representations, Problem Solving, and Decision Making - Foundations for Designing User-Centered Systems - page 179

Table 6.3 Problem solving requirements and several potential difficulties
Starting goal state Can't tell if the system is at the starting state

Goal state Can't tell directly what is a goal state

Don't know the goal state

Intermediate states Can't tell what state the system is in

Can't tell distance to goal state
Can't tell direction to goal state

Operators Can't tell what are the operators

Can't tell if operator had an effect
Operators are difficult to perform (physically or mentally)
Have to apply a lot of operators
Can't tell which operators are safe/appropriate to use

6.3.5 Summary of Problem Solving with Implications
for System Design

When you are creating systems, it is worth considering whether users will be
problem solving and learning, or will they all be experts and be performing routine
behavior all the time. In nearly every interface (although there are exceptions),
some of the users some of the time will be problem solving. Small changes can
often make it easier for them to problem solve.
Users will have to resort to problem solving with systems upon occasion. To
help the users, you should support them in their problem solving (unless you are
building games, when you may wish to make it more difficult deliberately) by
making it obvious which operations can be performed in the current context, for
example.
Making any aspect of problem solving more difficult will make an interface
more difficult in several ways, as indicated by Table 6.3 . You can make the user's
life easier in several ways. These include making the state of the system visible,
making the available operators known to the users (or enabling them to be learned
easily), and having operators that can be applied physically or mentally. In some
cases this may simply mean making the buttons bigger or the mouse-clickable
regions easier to grab. The constraints on the application of operators should be
consistent with the user's mental model, and the constraints should be visible or
knowable. The results of applying the operators should be provided to the user.

6.4 Decision Making

Decision making is the result of problem solving. Where the amount of problem
solving required is quite small, the problems solving and decision making may
appear to blur together. Decisions can be small or quite large. They range from
which button to push to which car to buy or where to land a failing airplane.