Why do systems of power change over time?

here is one example The PSA is a theory of change, meant to locate a programme, project, or campaign within a wider analysis of how change comes about. There are two ways to use it: by looking backwards, in order to explore past stories of change; and by looking forward, by learning to ‘expect the unexpected’. The PSA suggests characteristics that activists should cultivate in order to flourish in complex systems, like curiosity, humility, self-awareness, and openness to a diversity of viewpoints.

Explanation:

over time veiw points change

hey u think u can me with a summary? ?

a is the indefinite article