From Pema Chödrön's The Places That Scare You, near the beginning of Chapter 12 ("Thinking Bigger"):

Whenever someone asked a certain Zen master how he was, he would always answer, "I'm okay." Finally one of his students said, "Roshi, how can you always be okay? Don't you ever have a bad day?" The Zen master answered, "Sure I do. On bad days, I'm okay. On good days, I'm also okay." This is equanimity.

_{^z - 2015-03-15}