See the Good
Everyone has times in their past that they look upon as "dark nights"—Tragedies or difficulties that were largely beyond their control and sometimes the direct result of other people's wrong choices or unloving actions. How people react to those wrongs determines whether they become bitter or better for them.
Those who have a hard time seeing any good in the difficult times they've been through usually become resentful and make themselves even more unhappy. Perhaps they were wronged, but if they love Jesus and know that He loves them, He could have and would have used those situations for their good in some way if they had let Him. "We know that all things work together for good to those who love God, to those who are the called according to His purpose" (Romans 8:28).
What greater triumph is there than to bring good out of bad?
The Lord was probably trying to use those circumstances to help them in some way, but they've missed the point or haven't benefited as He intended. It's very possible that in many of these cases that people look back on as "mistakes," the circumstances were used or even engineered by the Lord in order to bring out the best in them, or to draw them closer to Him, or to teach them something valuable, or even just as a test. It's not that the Lord wanted these things to happen; He wants only the best for His children. But since they did happen, He wanted to turn them to good. That's the way the Lord is—He can and will turn anything to good, if we'll let Him.
Finding the good in a bad situation isn't just a "glad game" exercise or a good idea; it's vital to our spiritual health. If we can't accept that there could be a silver lining to some of the rain clouds of our past, then we'll probably never fully forgive and forget those things, and that can lead to bitterness, which is severely debilitating to your spirit.
For this reason it's vital that we not allow ourselves to look back at any situation, no matter how terrible it was, remembering only the bad. It may not be our favorite memory, it may even be painful, but if we'll ask the Lord specifically how He would like to use that situation for good, then He can set us free from that bitterness or other ill feelings and bring about beautiful victories.
What greater triumph is there than to bring good out of bad? That's the ultimate way to conquer our past hurts—not by bitterness and thoughts of revenge, but by allowing the Lord to make us better on account of it.