Answer:
I can be simple or I can be complex. I can be found in this riddle or in everyday life. I can be shapes or even colors.
Flat as a leaf, round as a ring; have two eyes, can't see a thing. What am I?
I am a box which holds keys but not locks. With the right combination, I may unlock your soul. What am I?
I am in the past, never in the future. I don't exist, but have existed. I saw what you saw, and this is what I will ever see. What am I?
I will go within you and destroy you. Only because you wanted me too
A little house full of meat, no door to go in and eat.