Bob: "Yup."
Christine: "Sure. And because this base reality exists, that proves I was right all along about Jesus: he did die for our sins."
Dhvan: "You mean it proves me right about Brahma."
Eris: "…the horned god."
Freya: "…Ragnarök."
and so on.
The key idea though is that if you make a dispassionate analysis of what this base reality must be, you find that it has certain 'attributes'. So for example, anything that has horns would not be good candidate for base reality since the contingent concept of 'horn' would need to be explained by, and derive its very existence from something much more simple. So that simpler thing would be the less bad candidate. Etc.