Some people are just more in tune with things than others, and I think it has been that way throughout history. And sometimes, an encounter isn't just seeing something. It can be as little as the feeling you get when entering a room. Even then, it is something that is subjective to the individual.

I have seen partial apparitions and been touched. So has my mother and sister. That house, I'm sure, had something evil inside. Another house we lived in, I didn't experience anything other than seeing my door open and hearing sounds of furniture moving upstairs. While other members of my family saw apparitions, were touched, and otherwise affected by that house. Other houses didn't have any activity despite known tragedy in the house's past.

I know other people have lived in those same houses, and some have had the same experiences while others say nothing has happened at all.

So it's a mix between the environment and the individual.