There are some tribes in the Amazon that are so inaccessible that the Western World still haven’t discovered them yet.
They live in the Amazon without a clue, basically. It’s inaccurate to say that they have no contact with the outside world themselves, as they probably conduct small amounts of trade with ‘locals’ who don’t really represent the Western World.
I saw this picture in the paper just over a year ago, about an Amazon tribe that covers itself in orange paint, who have spotted an overflying plane above them, and tried to shoot it down with their bow and arrows,

The thing is, they hate white people, mostly stemming from their ancestory who experienced white people colonising their land and killing their people, so the small groups of explorers unlucky enough to discover these tribes (its hard to get big groups so far into the Amazon), are slaughtered.