ALLOWING OURSELVES TO MOURN develops our capacity to feel life’s joys. I believe that positive and negative emotions are two sides of the same coin. Of course, many of us would prefer to experience and deal with only positive feelings. We often feel uncomfortable with our own or others’ sadness, anger, disappointments, fears. … As we learn to feel all our feelings, we explore what it means to be fully human, to be all that God created us to be.

- Mary Lou Redding
The Power of a Focused Heart: 8 Lessons from the Beatitudes

From p. 31 of The Power of a Focused Heart: 8 Life Lessons from the Beatitudes by Mary Lou Redding. Copyright (c) 2006


And also this similar thought: God turns you from one feeling to another and teaches by means of opposites, so that you have two wings to fly, not one.
— Rumi quoted in Love Is a Fire by Llewellyn Vaughan-Lee
by way of Spirituality and Practice