The boundary separating system and environment is not like a physical boundary that can looked across. It is more accurately described as a horizon. The system can assume that something exists beyond the horizon, but it can never be seen. Indeed, it operates on the assumption that something else is out there.
This is about first- and second-order observation. Second-order observation observes both sides of the first-order observer’s distinction. Only the second-order observer can see across the first-order observer’s horizon.
Inevitably, we are confronted with a paradox in the search for unity, that is, with the demand to continue. For observers are autopoietic systems that can only produce their operations on the assumption that other operations will follow. The world is therefore an endless world, a “horizon” always holding out the prospect of other possibilities.
(A Systems Theory of Religion, 50)
This is also why consciousness cannot conceive of its own death or ending. It cannot operate without the assumption that something else is always coming.