What makes your decision difficult?
Difficulty can arise in at least four ways, Scope, Conflicting Goals, Uncertainty and Complexity.
ScopeYou are not sure who should be involved, who should make the decision. It is not clear what should be taken into account.
Conflicting GoalsIf there are several decision makers they may have different objectives. You may need to take into account the views of other interested parties.
Even with a single decision maker there may be conflicting goals. For example when choosing a car you may want high speed but low insurance costs. However it is likely that the higher the top speed the more the insurance will cost. You will have to make a trade off between speed and insurance costs.
Multi-criterion decision analysis (MCDA) can help you make complex trade offs between conflicting goals. To see how this is done, follow the walk-through tutorial.
Uncertainty or riskThe outcomes may depend on factors outside your control, such as the weather or interest rates.
Complexity of calculationEven if you have a single objective and know what all the outcomes are there may be too many alternatives to actually be able to find the best. An example of this is the travelling salesman problem.
A travelling salesman wants to minimise his journey distance when visiting a number of towns. There are so many possible routes that it may not be possible to find the shortest.