… the way out transfers from the tunnel to the ceiling prior to never having been.
Continuing through Beckett, Modernism and the Material Imagination by Steven Connor (2014):
… Beckett’s work often deals in notions, propositions, data, in the strict sense of that which is given. ‘That then is the proposition. To one on his back in the dark, a voice tells of a past.’ Getting, or keeping things going, is a matter of ‘notions’ being maintained.
… The first thing we learn [in The Lost Ones] about the belief is that it fluctuates, but with a sort of permanently recurring rhythm: ‘From time immemorial rumor has it or better still the notion is abroad that there exists a way out. Those who no longer believe so are not immune from believing so again in accordance with the notion requiring as long as it holds that here all should die but in so gradual and to put it plainly so fluctuant a manner as to escape the notice even of a visitor.’ The belief also gives rise to sectarian rivalry, rendered with mock-scholarly solemnity as though they were the terms of a medieval disquisition:
Regarding the nature of this way out and of its location two opinions divide without opposing all those still loyal to that old belief. One school swears by a secret passage branching from one of the tunnels and leading in the words of the poet to nature’s sanctuaries. The other dreams of a trapdoor hidden in the hub of the ceiling giving access to a flue at the end of which the sun and other stars would still be shining.
… though we have earlier been assured that ‘it is doubtful that such a one exists,’ the conviction grows that there is a logic, and even a providence, in this shift from belief in a way out via the tunnels to a way out through the roof:
For those who believe in a way out possible of access as via a tunnel it would be and even without any thought of putting it to account may be tempted by its quest. Whereas the partisans of the trapdoor are spared this demon by the fact that the hub of the ceiling is out of reach. Thus by insensible degrees the way out transfers from the tunnel to the ceiling prior to never having been.