It appears that I can only focus on one thing at a time.
This can be a number of things to "choose from" like Fear, Anger, Joy, Depression.
When I am not thinking about the number two, it does not mean that it does not exist, just that I am not focusing on it right now. However, as soon as I need to, represent in my mind, the number of apple slices I have when cutting an apple in half, the number two receives my focus.
Therefore Fear requires my "Focus". When I am not thinking about it, that doesn't mean that it no longer exists. However, when it does not have my focus, I don't feel its negative effects.
While I don't have full control over what receives my Focus, I do have some influence in the matter.
The same with Joy, Gratitude, and other 'positive' things that also compete for my Focus. I can make a conscious decision to Focus on these things. Perhaps in the morning before my day begins. Perhaps in the midst of a stressful episode.