system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:Why do we forget most of our dreams?
gpt
If you wake up unnaturally (I.e with an alarm clock),  you have a chance of remembering your dream you were just in. You don't remember dreams when you wake up naturally because your brain has shut off the "dream machine" in preparation for waking up,  and discards the dreams from your short term memory because they are not needed and not meant to be stored with conscious thought/experiences.  

When you're sleeping, your subconscious brain is entertaining itself and working through data/experiences... its basically playing, and the toys are the elements in your dreams (people, places, things, conversations, feelings..) and the playroom is your memory. When you wake up naturally, your brain puts away all it's toys and closes the chest, so there aren't a bunch of dream elements laying all over the floor of your memory.  When you wake up suddenly, the toys are all over the place, scattered across the playroom/your memory.