"..just imagine some natives in Borneo speculating..."

But we 'could' take someone from Borneo, and given a bit of time, show & demonstrate the basic principles involved, and at least get them to understand it is not just witchcraft or illusions.

Of course we dare not say that we have learned all the possible 'principles' of physics, but neither should we assume that there ARE principles and techniques that would allow travel between the stars...or galaxies!

There's fine line between an 'open mind' and gullibility. I try to get as close to it as I can without committing myself to 'belief' in stuff that I have fervently wished for these 60 years I have read Sci-fi.....