Next time a door opens when there is no draft or another door being opened, just think about what might be about to walk through. There are entities that only partially exist.
They are all around us and we don't notice them that often, but sometimes, something will move without being touched or a sound will appear from nowhere.
Sometimes there are logical explanations behind this. But every now and then they act upon the world, they come for the weak and fragile to claim their soul. Take it to death itself... and remember nothing in life is certain, except death.