In the JW mindset, the Bible is God’s word, and therefore the ultimate proof and trumps all other forms of evidence, no matter how concrete.
In truth, their basis for reality is the Watchtower interpretation of a few dozen verse which are nearly always presented out of context. There is no true exegesis. If the Bible itself contradicts Watchtower interpretation, their interpretation always wins.
Interpretation of the Bible is decided by the Governing Body. It takes a two thirds majority to change any teaching. If a JW disagrees they can find themselves in a secret backroom trial called a judicial committee, and they could be disfellowshipped for apostasy or “sowing divisions” and find themselves shunned by their family and friends.
JWs have absolute trust in the Governing Body and their representatives.
Even though they are not infallible, the mythos is they are “spirit directed”. Even if they get some things wrong occasionally, they’ve are viewed with the best of intentions. And besides God and Jesus chose them. If God and Jesus trust me…so should we!