Let us begin by considering a situation which calls for a choice. Imagine yourself as the owner of a large business, faced with the prospect of meeting or not with a possible client who can bring valuable business but also happens to be the archenemy of your best friend, and proceeding or not with a particular deal.... Even in this caricature you will recognize the sort of quandary we face most every day. How do you resolve the impasse? How do you sort out the questions inherent in the images before your mind's eye?
There are at least two distinct possibilities: the first is drawn from a traditional "high-reason" view of decision making; the second from the "somatic-marker hypothesis."
The "high-reason" view, which is none other than the common-sense view, assumes that when we are at our decision-making best, we are the pride and joy of Plato, Descartes and Kant. Formal logic will, by itself, get us to the best available solution for any problem. An important aspect of the rationalist conception is that to obtain the best results, emotions must be kept out. Rational processing must be unencumbered by passion.
Basically, in the high-reason view, you take the different scenarios apart and to use current managerial parlance you perform a cost/benefit analysis of each of them. Keeping in mind "subjective expected utility," which is the thing you want to maximize, you infer logically what is good and what is bad.... You are, in fact, faced with a complex calculation ... and burdened with the need to compare results of a different nature which somehow must be translated into a common currency for the comparison to make any sense at all. A substantial part of this calculation will depend on the continued generation of yet more imaginary scenarios, built on visual and auditory patterns, among others, and also on the continued generation of verbal narratives which accompany those scenarios, and which are essential to keep the process of logical inference going.
Now let me submit that if this strategy is the only one you have available, rationality, as described above, is not going to work. At best, your decision will take an inordinately long time, far more than acceptable if you are to get anything else done that day. At worst, you may not even end up with a decision at all because you will get lost in the byways of your calculation. Why? Because it will not be easy to hold in memory the many ledgers of losses and gains that you need to consult for comparisons. The representations of intermediate steps, which you have put on hold and now need to inspect in order to translate them in whatever symbolic form required to proceed with your logical inferences, are simply going to vanish from the memory slate. You will lose track. Attention and working memory have a limited capacity. In the end, if purely rational calculation is how your mind normally operates, you might choose incorrectly and live to regret the error, or simply give up trying, in frustration.
What the experience with [brain-damaged] patients such as Elliot suggests is that the cool strategy advocated by Kant, among others, has far more to do with the way patients with prefrontal damage go about deciding than with how normals usually operate....
It is also important to note that the flaws of the common-sense view are not confined to the issue of limited memory capacity. Even with paper and pencil to hold the necessary knowledge in place, the reasoning strategies themselves are fraught with weaknesses, as Amos Tversky and Daniel Kahnerman have demonstrated.... Nonetheless, our brains can often decide well, in seconds, or minutes, depending on the time frame we set as appropriate for the goal we want to achieve, and if they can do so, they must do the marvelous job with more than just pure reason. An alternative view is needed.
Damasio's alternative view is his "somatic-marker hypothesis," where emotions figure as warning signals to help guide reasoning and make it more efficient:
There is still room for using a cost/benefit analysis and proper deductive competence, but only after the automated step [provided by the somatic marker] drastically reduces the number of options [explains Damasio]. Somatic markers may not be sufficient for normal human decision-making since a subsequent process of reasoning and final selection will still take place in many though not all instances. Somatic markers probably increase the accuracy and efficiency of the decision process. Their absence reduces [its efficiency]....
The work of Amos Tversky and Daniel Kahneman demostrates that the objective reasoning we employ in day-to-day decisions is far less effective than it seems and than it ought to be. To put it simply, our reasoning strategies are defective and Stuart Sutherland strikes an important chord when he talks about irrationality as an "enemy within." But even it our reasoning strategies were perfectly tuned, it appears, they would not cope well with the uncertainty and complexity of personal and social problems. The fragile instruments of rationality need special assistance...
But while biological drives and emotion may give rise to irrationality in some circumstances, they are indispensable in others. Biological drives and the automated somatic-marker mechanism that relies on them are essential for some rational behaviors, especially in the personal and social domains... [Descartes' Error, p. 170-200]