Since our echo-chambered teenager encountered the echo chamber’s beliefs first, those beliefs will inform how she interprets all future evidence.
to put it simply, from the day you're born your beliefs in life are dependent on what you're exposed/subjected to and will inevitably inform your future path in life.
For those who have not been raised within an echo chamber, perhaps it would take some significant intellectual vice to enter into one – perhaps intellectual laziness or a preference for security over truth.
everything is an echo chamber; the concept itself is so meta its no surprise that by simply believing in something you are unknowingly (or knowingly) submitting yourself to an infinite world of echo chambers