Jehovah's Witnesses say they are 'in the truth'. Everyone outside their organization is 'out of the truth'.
How can they be so sure of their beliefs? Because the founders of the Jehovah's Witnesses claimed to be 'anointed' with God's Holy Spirit.
Early Watchtower leaders were very charismatic and convincing. They were able to stir up the masses and gather a huge following. They did this by making frightening predictions about armageddon and by exaggerating the truth about their relationship with God. These leaders believed they were God's chosen ones and everyone who followed them would be spared when the end of the world comes.
It's possible that early Watchtower leaders were not thinking straight. They may have been influenced by past religious beliefs. Or they could have been mentally or emotionally imbalanced causing them to do and say things normal individuals would not do and say.
Early JW's believed Watchtower leaders. They taught their children to fear the Watchtower's message because they believed it came from God. Their children grew up and became leaders in the organization. They taught their children the same things they were taught.
Thus the Jehovah's Witnesses have perpetuated a religious tradition that extends down several generations. Their 'past religious beliefs' are influencing what they believe today.
Even today the anointed Governing Body of JW's might not be thinking straight based on what the Watchtower says about anointed individuals.
Notice what the Watchtower admits about the 144,000 'anointed' JW's who believe they're the only ones who have been chosen by God to go to heaven.
'A number of factors—including past religious beliefs or even mental or emotional imbalance—might cause some to assume mistakenly that they have the heavenly calling. We thus have no way of knowing the exact number of anointed ones on earth; nor do we need to know.' WT, Aug 15, 2011, page 22
Based on what the Watchtower says, just because someone claims to be anointed doesn't mean they are. They could be mistaken. Thus even though the Governing Body of JW's claims to be anointed doesn't mean they are.
JW's today know what they know but they don't know why. They have 'faith' like many religious groups have. Even though JW's say they have 'the truth', it would be more honest to say they have faith based on years of religious programming.