Sometimes people think that their subconscious is letting them see what's going to happen in future in their dreams. It may not be that simple as that, and people also may misinterpret what they are seeing while they are asleep. There isn't any science to dreams either, however they are a mystery. Dreams at best are sometimes hints to some event that has link with reality or which is already planned or is to happen according to the logical sequence or could happen. Dreams mostly could guide someone's psyche to better understand the people concerned or things concerned or certain realities of life. If someone thinks dreams told you only this will happen, they are wrong and mostly weak people who lack insight into their lives.

Disclaimer: This is in no way a result of some research or study, rather what I consider as the flawed approach to dreams and their interpretation. It is also my own observation that whatever is responsible for creating dreams also plays tricks on people's minds. So it is better to find a practical solution to your real problems rather than making impractical dreams defining realities for you.