Truth is a matter of perception and belief. Most of the time what we believe is false. Things that are 'true' can never change. If we change 'the truth', our new beliefs automatically become false. If our new beliefs are true, then our old beliefs were false.
Children and teenagers know everything. The world is simple, one sided, and crystal clear based on their limited knowledge. However as children grow up and gain wisdom, they understand that the more they know, the less they know for sure. Wise people do not always know what is true and what is false. Why? Because wise people see things from many different perspectives.
Why do the Jehovah's Witnesses say they have the truth if their beliefs can change in the future? Critics say it's part of their religious programming. If beliefs can change, the are not 'the truth'. They are merely viewpoints, interpretations of the Bible, and perspectives that change with time. See Mind Control