Psychologists document choice blindness:

As anyone who has ever been in a verbal disagreement can attest, people tend to give elaborate justifications for their decisions, which we have every reason to believe are nothing more than rationalisations after the event. …

In one recent study we invited supermarket customers to choose between two paired varieties of jam and tea. In order to switch each participant's choice without them noticing, we created two sets of "magical" jars, with lids at both ends and a divider inside. The jars looked normal, but were designed to hold one variety of jam or tea at each end, and could easily be flipped over.

Immediately after the participants chose, we asked them to taste their choice again and tell us verbally why they made that choice. Before they did, we turned over the sample containers, so the tasters were given the opposite of what they had intended in their selection. Strikingly, people detected no more than a third of all these trick trials. Even when we switched such remarkably different flavours as spicy cinnamon and apple for bitter grapefruit jam, the participants spotted less than half of all switches.

We have also documented this kind of effect when we simulate online shopping for consumer products such as laptops or cellphones, and even apartments. Our latest tests are exploring moral and political decisions, a domain where reflection and deliberation are supposed to play a central role, but which we believe is perfectly suited to investigating using choice blindness.

Throughout our experiments, as well as registering whether our volunteers noticed that they had been presented with the alternative they did not choose, we also quizzed them about their beliefs about their decision processes. How did they think they would feel if they had been exposed to a study like ours? Did they think they would have noticed the switches? Consistently, between 80 and 90 per cent of people said that they believed they would have noticed something was wrong.

If we know little about the real reasons for our choices, how can we know they are good reasons?  If we disagree with someone else about a good choice, how can we have much confidence that our reasons are better than theirs?   Can the blind reasonably feel confident in leading the blind?