Explanation:

- Observation: Managers and theorists have carefully watched and studied successful management practices over time. This helps in understanding which principles work well in specific situations.

- Experimentation: Some management theories are derived from experimental approaches, where different strategies are tested to see what yields the best results.

- Personal Experiences of the Manager: Managers often develop insights and best practices based on their own experiences and challenges faced during their careers.

- All of the above: The principles of management are indeed developed through a combination of observation, experimentation, and personal managerial experiences. Each source contributes valuable insights that shape effective management practices.