What we have come to accept as reality and the way things are, forms our beliefs. They are strongly influenced by our environment and this has many implications on our beliefs and what we chose to believe in.
Our values are developed over time, they are dynamic and change over time, they change with age, with new influences and new directions or decisions.
A persons set of personal values and beliefs are often guarded and hard to reach or influence. And on the other hand, other people can be easily influenced by others. Religion and the effects of preaching are great examples of how some people will change their entire belief system based on someone else's belief system.
People have their own unique set of values and belief systems. Yet many share the traits of common beliefs. For example among the scientific community, what has been proven is then considered fact and is commonly believed or accepted and valued.