They say that there are people who can predict the future in dreams - that they dream of things to come. They say that all dreams have meaning. Some believe that dreams are sent by the gods as messages to mortals. Some slightly more rational people speculate that dreams are the mind's way of working out problems in our lives, while we sleep. What is the true value of a dream? Perhaps evolutionary psychology can give us the answer.
Evolution favours creatures that have some advantage or other. If one set of genes gave people a definite advantage in life, then this set would become very common after a while. Even if the advantage were slight, or came with costs, if it caused people to do better in life and reproduce more, then in time most people would end up with it.
I think that you will agree that a person who could predict the future better than others would be likely to do better than others. If dreams gave a person even a slightly better chance of knowing what to be wary of, or what opportunities to grab, then, over the course of a lifetime, he'd be at a strong advantage over lesser folk. If his dreams proved accurate over half the time, he'd be an idiot not to pay close attention to them always. Even if they were right less than half the time, they might prove on numerous occasions to be useful warnings of something or other.
Once genes had created a mechanism in humans that gave them advantageous dreams, then evolution would act to refine this trait. As generations went by, Man would improve his dreaming. Dreams would become ever more useful.
But there's a big snag. People cannot act on their dreams if they cannot remember them. People dream a few times in a typical night, and most of the time, people remember nothing of the dreams they have save perhaps those they had shortly before awakening. Even then, these memories fade very quickly. It is as though the brain acts deliberately to get rid of these unhelpful memories.
Why would the norm be to forget dreams? Surely the simplest and best explanation is that dreams are a load of useless rubbish, which would hinder a person if heeded. If a person tries hard to remember a dream, he will still probably fail. The brain really seems to be acting against the will of the mind here. Evolution has favoured a brain that does not heed dreams, and has evolved a mechanism for wiping the scrawl off the mental blackboard, to make room for waking rationality. If dreams were useful, then the people who could make the best use of them would succeed the most, and so people would have evolved to remember dreams, but instead the fact seems to be that people have evolved to forget them.
Is it terribly surprising that a dream in which you are a pig that can breath underwater, looking for spoons, which then turns into someone who is a sort of cross between your brother and Spike Milligan, who then moves into your old house which now has a conservatory that your real previous house lacked, and who then sets fire to his shoes before walking to Portugal, is not a useful dream on which to base your life? In order to be advantageous, dreams have to be better at predicting life, and better at advising you on how to act than your waking mind. They are not. Your waking mind has access to much more accurate information on the way the world is, and can make far more rational decisions, and can concentrate, prioritise, infer, experiment, recall, and apply logic enormously better than your subconscious dreaming mind, cut off from reality and drifting randomly.
If dreams were better at informing decisions than our waking minds, then they would be the things we preferred, but they are not. Since our waking minds are better than our dreams at informing decisions, evolution has favoured people who have not acted upon their dreams. Accordingly, people forget their dreams. That way, evolution has removed the danger of a person's becoming a dream-following fool. Of course, some people while awake think that they can remember dreams that they had years ago, but I suspect that what they are really remembering is the conscious act of remembering the dreams that occurred after waking.
"But," I can hear someone in my imagination saying, "I can remember a dream I had four years ago, in which I got a 'phone call offering me a new job, and soon after I woke up, I got a call from my current boss who told me I was promoted. This shows that dreams can be useful. That's your theory in ruins, mate." Well, what this notional man actually remembers, I suggest, is the thought that went through his mind when he got the call, which was "Wow! I just dreamt this!" The moment was a significant one in his life, and the event of the call reminded him of a dream that he would otherwise have forgotten. Note that the man did not have to alter the choices he made in life as a result of his dream. Instead, he was reminded of a dream, and he made the decision that he would have made had he not had the dream: he accepted the job. If the dream had altered his choice, and had turned out to be genuinely useful, then that would have been something different.
The few occasions when it appears that a dream has had some bearing on reality should not surprise us. We do not dream all the time about things outside of human experience. Most dreams have some recognisable similarity with reality. We dream of places and people we know, although often inaccurate representations of them. If we dream that we are in a familiar place, we can accept in the dream that it is the place we know if it has the same emotional feel of the place, even if in the real version, the sky isn't orange, and the windows aren't made out of treacle. Given how vague the dream-world can be and yet how we can accept it, and given that we dream most nights for our whole lives, the chances against some dreams never having any coincidence with what happens in reality are ten to the power of a solicitor's fee to one against.
So, enjoy them, but forget them.