where stupid dreams comes from

I believe it was Sigmund Freud who said that dream comes from memories in our unconscious mind. He was right. Sometimes when we are asleep, we begin to remember stuff from our unconscious memories (stuffs that we had sensed but did not took a big notice of or that are not of high-priorities) at random. e.g a book U saw briefly on the Library shelve, the voice of the 6 O-clock news lady, the smell of a co-workers cologne or the funny shape of a friends head. Our Brain would throw all these random memories together and make a narrative smoothie out of em. This smoothie is dream.
For the above example, you might come up with a dream about your friend reading the 6 o-clock news to you out of that book you saw at the library, but he is smelling exactly like your co-worker. This is why dreams don't make sense most of the time. but this is just my theory.