I do not believe that people are capable of rational thought when it comes to making decisions in their own lives. People believe that are behaving rationally and have thought things out, of course, but when major decisions are made—who to marry, where to live, what career to pursue, what college to attend, people's minds simply cannot cope with the complexity. When they try to rationally analyze potential options, their unconscious, emotional thoughts take over and make the choice for them.
As an example of what I mean consider a friend of mine who was told to select a boat as a wedding present by his father in law. He chose a very peculiar boat which caused a real rift between him and his bride. She had expected a luxury cruiser, which is what his father in law had intended. Instead he selected a very rough boat that he could fashion as he chose. As he was an engineer his primary concern was how it would handle open ocean and he made sure the engines were special ones that could be easily gotten at and that the boat rode very low in the water. When he was finished he created a very functional but very ugly and uncomfortable boat.
Now I have ridden with him on his boat many times. Always he tells me about its wonderful features that make it a rugged and very useful boat. But, the other day, as we were about to start a trip, he started talking about how pretty he thought his boat was, how he liked the wood, the general placement of things, and the way the rooms fit together. I asked him if he was describing a boat that he had been familiar with as a child and suggested that maybe this boat was really a copy of some boat he knew as a kid. He said, after some thought, that that was exactly the case, there had been a boat like in his childhood and he had liked it a great deal.
While he was arguing with his father in law, his wife, and nearly everyone he knew about his boat, defending his decision with all the logic he could muster, destroying the very conceptions of boats they had in mind, the simple truth was his unconscious mind was ruling the decision making process. It wanted what it knew and loved, too bad for the conscious which had to figure how to explain this to everybody else.
Of course, psychoanalysts have made a living on trying to figure out why people make the decisions they do. The problem with psychoanalysis is that it purports to be able to cure people. This possibility I doubt very much. Freud was a doctor so I guess he got paid to fix things and got carried away. But his view of the unconscious basis of decision making was essentially correct. We do not know how we decide things, and in a sense we don't really care. Decisions are made for us by our unconscious, the conscious is in charge of making up reasons for those decisions which sound rational. We can, on the other hand, think rationally about the choices that other people make. We can do this because we do not know and are not trying to satisfy unconscious needs and childhood fantasies. As for making good decisions in our lives, when we do it is mostly random. We are always operating with too little information consciously and way too much unconsciously.