What makes one abandon what they believe?

I have had that question in my mind the last couple of days, ever since i read a post on this blog
http://www.nataliercollins.com/weblog/2005/04/more-for-mandy.html
Why would someone who believes something leave it of fall away from it? I have been thinking about that, and generally there are two reasons. Either they never truly believed what they thought they believed, meaning they were just following and they finally came to a realization that they never really believed and they move onto a different path. Or they are offended in some way that makes them leave. They can be offended by someone or the something they believe in. That also begs the question of what is the Truth. In that posting, Mandy stated that it is True. It is true to her, that doesn't make true to natalie. Truth is relative to the person, just as morality is. One can not bash on another because they believe they have the truth. This life is to aquire truth and it can only be aquired by serious introspection and thought by one self. Not being told by someone else. Yes we may here the truth from someone, but in order to embrace it we must make it apart of ourselves. I do beliee there is an Absolute truth and that it is God who can lead us to it, but we must allow him to do that and be open to whatever he may say. He is the ultimate source of truth and we must ask with sincerity if we believe something to be truth and he will in the end give us the answer.