A rational decision model presupposes that there is one best outcome. Because of this it is sometimes called an optimizing decision making model. The search for perfection is frequently a factor in actually delaying making a decision.
Such a model also presupposes that it is possible to consider every option and also to know the future consequences of each. While many would like to think they know what will happen, the universe often has other plans!
It is also limited by the cognitive abilities of the person making the decision; how good is their memory? how good is their imagination? The criteria themselves, of course, will be subjective and may be difficult to compare. These models require a great deal of time and a great deal of information. And, of course, a rational decision making model attempts to negate the role of emotions in decision making.