Keeping the faith

Philosophies, religions, beliefs, sciences all have a theme. Like music. One principle or idea around which it is built. Like how various pieces are put together to a symphony.
It is so that most people live their lives with certain beliefs. What if along the line you realise that the pieces you put together to form the symphony were wrong. That the way every little note is percieved changes so much that your grand symphony is reduced to a cacophony?
There is a certain dialogue that takes place in Maugham's Of human bondage which might illustrate.
The essence of the particular passage is that as time passes, perception and truths change too. For instance, St. Augustine believed that the earth was flat. He believed that with his generation.
We now believe otherwise. Extend that to faith, personal beliefs and religion.
We build all our lives around this, our perception of the right. Or wrong.
How do we know if we have the truth now? How do you believe anything at all?
What does one put her faith in? Does it just boil down to one's highest truth?
Is God playing dice with the universe?