Well, if you think about it, most of us don't remember our dreams at all, we only remember some fragments of them for the first 10 minutes when we wake up, then we completely forget about them, and this process continues every single morning.
The reason for this is simple:
When you wake up, you are still partially in-tune with your subconscious mind. You know that feeling of disorientation and slowness when you wake up?
Your conscious mind is slowly “booting up”, like a computer. During this time you have a brief shadow memory window. During this time you can access some of your shadow memory; it's usually at this time that fragments of our dreams still float around our mind aimlessly. As we get up, take a shower and eat breakfast it seems that these memories quickly “deteriorate” and fly out of our minds forever. What's actually happening is your conscious mind is gaining full awareness, and you lose the connection with your subconscious memory.
Because our conscious mind takes over when we wake up, our mind labels the brief half-real fragments of shadow memory as “not important”. When we reflect on them in the 10 minutes after waking up it only seems like our dream(s) may have been a few minutes long.