What kind of conceptual tension does Zada grapple with on his quest to find the Sasquatch?

Zada grapples with the conceptual tension between existence and non-existence which he initially sees as the driving question on his quest. The tension arises because Zada notices that if many people believe in a thing, even without physical evidence of that thing's 'reality' as such, then that thing begins to take on an existence regardless of proof against the contrary. The existence in question, of course, may not be physical, but rather an existence in the human mind which is no less real or impactful. This tension nags at Zada throughout book as he seeks to reconcile himself with the fact that no physical evidence of the Sasquatch can be pinpointed even as he 'encounters' the Sasquatch around every corner in a psychological and spiritual sense.

How does Alvina aid Zada in his quest for information?