When a program begins, the program is perceived as an obvious success.
A program to be successful needs to manage risks properly.
As programs are collections of projects, managing program risks means also managing some risks that arise from within projects.
At the same time, programs have risks that are at program level.
The remaining program risks could be external to the program (e.g. related to organizational or strategic aspects).
Keep in mind: when a program starts you need to determine the strategy to assess all program risks.