Focus on What You Can Control

When you are grieved about anything external it is not the thing itself which afflicts you, but your judgement about it. This judgement it is in your power to efface. If you are grieved about anything in your own disposition, who can prevent you from correcting your principles of life? If you are grieved because you do not set about some work which seems to you sound and virtuous, go about it effectually rather than grieve that it is undone.

Often times, the anxiety and unhappiness that people experience comes from focusing on things that they can not control. For example, things that other people say or do, or the outcome of external situations.

Dwelling on these things that are out of your control is a waste of time. Instead, it is better to focus on things that you can control, namely, your own thoughts, and how you interpret the world around you.

It is your thoughts and opinions that make a situation good or bad, not the situation itself being inherently good or bad.

References

Meditations by Marcus Aurelius