This is one of the most important questions as throughout time much of the reality has become myth. The Ramayan and Mahabharat are considered epics and historic however most of the Purans are considered myths. In Mahabharat Bhagwan Krishn is mentioned all over places. In the Puran he is also mentioned so why then has Puran become a mythology and Mahabharat a historic epic? Much of the problem exists because many of the stories in the Puran are repeated and tend to be different from one Puran to the next. In one you will see Ram worshiping Shiv in another Shiv will worship Ram. So you will see one aspect of God higher in one Puran then the other. You will see Vishnu as the top most God in Vishnu Puran and see Bhagwan Shiv as top most GOD in Shiv Puran. Mata Shakti is the top most God in Devi Puran. So how can this be?