From the viewpoint of BELIEFS all doubts are disastrous. From the viewpoint of FAITH, doubt is the indispensable stimulant. To lose one's BELIEFS may not be a loss but a gain: an opportunity. "When the heart weeps for what it has lost, the spirit laughs for what it has gained," is an ancient Sufi saying. To lose one's FAITH, however, is catastrophic; the loss of this vital human constituent means mutilation, dehumanization, cynicism, nihilism.
I have found that the greatest degree of inner tranquility comes from the development of love and compassion. The more we care for the happiness of others, the greater is our own sense of well-being. Cultivating a close, warmhearted feeling for others automatically puts the mind at ease.