It passes from community to community. Pieces are added on. Other pieces are dropped. It takes on new and old meanings as it travels, based on the needs and values of the community. The difference between a story and policy is that a story can always be changed.
Public policy becomes, at some point, the law passed or the budget utilized.
It can also be altered, but changing an agreed upon policy is not easy. This is also because the dynamic process of public policy design, with public input and debate is taken very seriously. And what takes a long time to define, test, debate and implement, should not be easily undone. Public policy can provide and enhance opportunity and access for people. It can be a major vehicle of democratic change for a nation.