Reality tunnel is a theory that, with a subconscious set of mental filters formed from beliefs and experiences, every individual interprets the same world differently, hence "Truth is in the eye of the beholder".
The idea does not necessarily imply that there is no objective truth; rather that our access to it is mediated through our senses, experience, conditioning, prior beliefs, and other non-objective factors. The implied individual world each person occupies is said to be their reality tunnel. The term can also apply to groups of people united by beliefs: we can speak of the fundamentalist Christian reality tunnel or the ontological naturalist reality tunnel.
A parallel can be seen in the psychological concept of confirmation bias—the human tendency to notice and assign significance to observations that confirm existing beliefs, while filtering out or rationalizing away observations that do not fit with prior beliefs and expectations. This helps to explain why reality tunnels are usually transparent to their inhabitants. While it seems most people take their beliefs to correspond to the "one true objective reality", Robert Anton Wilson emphasizes that each person's reality tunnel is their own artistic creation, whether they realize it or not.
We don't see things as they are; we see them as we are. – Anaïs Nin
Also touched upon in constructivism and by lacan