The Circle of Control mental model emphasizes focusing energy on things within one's control and accepting those that are beyond control.
This mental model suggests that it is more effective and healthy to spend time and energy on aspects of our lives that we can directly influence or control. For instance, rather than worrying about a looming economic crisis (something beyond our control), we should maybe focus more on enhancing our skills, budgeting, and saving money (things within our control). Thus the model encourages proactive behaviour, rather than reactive behaviour.
In the Circle of Control, proactive people focus their efforts. This focus results in a series of positive proactive thoughts, actions, and outcomes.