Deviations from the rational model of the decision making process are mostly due to behavioral factors?

Decision making by people, whether using rational or subjective approaches, are part of human behavior. Thus the choice between alternative approaches to decision making is also a part of decision making behavior affected by behavioral influences or factors. Thus all type of decision making behavior including the rational decision making process are influenced by behavioral factors. But there is a difference of degrees. Rational decision process will involve a greater proportion of objective considerations and clearly laid down decision making algorithms and less of subjective elements, as compared to decision  that are based on personal judgements or subjective preferences.

If a decision is completely devoid of human elements of personal judgement or some other subjective, then it has to be a decision that can be taken by an automated system without human involvement. For example decision that are based entirely on some mathematical techniques such as EOQ or linear programming can be taken in a suitably programmed computer system without human intervention.

Before I close, I thing it will be appropriate for me to draw attention towards the fact that the use of the phrase "Deviation from rational model of decision making" creates some wrong impression that deviation from rational model of decision making is necessarily undesirable.

A rational decision is one which is based on a clearly defined objective rationale. The quality of a rational is only as good as the quality and applicability of the rationale used. A rational decision based on wrong data or wrong decision making technique, can be much worse than the subjective decision of an experienced person.As a matter of fact, in management most of the important decision requires more of subjective elements rather than the objective elements of rational decision making.