Romans 8:28 And we know that for those who love God all things work together for good, for those who are called according to his purpose.
As with many people, this is a verse I have clung to in hard times. We know God is good and He is working for our good. We just won't always know His purposes. He is a God of wisdom and that wisdom is His, not ours.
Ecclesiastes 11:5 As you do not know the way the spirit comes to the bones in the womb of a woman with child, so you do not know the work of God who makes everything. In His wisdom He does not reveal all of His ways to us. We may never know why He allows certain evil or suffering in our lives, but we can know that He is working in our lives for our good.
This is where faith comes in to play. Galatians 5: 5-6 For through the Spirit, by faith, we ourselves eagerly wait for the hope of righteousness. 6 For in Christ Jesus neither circumcision nor uncircumcision counts for anything, but only faith working through love.