There is a Taoist story of an old farmer who had worked his crops for many years. One day his horse ran away. Upon hearing the news, his neighbors came to visit. "Such bad luck," they said sympathetically.
I know I say this over and over but it's only because it is such a profound truth: God is the Source of all that is, therefore nothing can exist that is not of God. So if everything that exists comes from the Divine, both 'good' and 'bad', 'light' and 'dark' are creations of God.
Older religious practices knew this to be true, and that is why we see the worship and reverence of Cthonic deities throughout history. But in modern times we relate fear and negativity to the 'darker' aspects of life, and subsequently find peace and hope in the 'lighter'. But we can see even in the Bible, God is the creator of all - and that includes 'evil'.
I form the light, and I create darkness. I bring prosperity and create disaster. I the Lord do all these things. - Isaiah 45:7
If we take the journey to the darkness - which is profoundly spiritual, and agonizingly unavoidable - as a time to strip away the ego and once again connect to that Divine spark that is within all of us, our soul, than we can learn and prosper (not only from the light, the good, the positive - but also) from the darkness.