The Serenity Prayer has been the single most repeated phrase I have ever used in my life! And what's better than it dangling off my keys to continually remind me!!
 
A common phrase adopted by recovery groups, treatments, and religious associations alike.
It is a reminder for us to take a pause, let go of our will, be aware of what we can do about a situation, and take action on that.
You can learn more about its origins & history here.