Many times parents blame themselves too much for the bad choices of their children. They forget that their children have become adults and could have chosen an evil path despite very good home training. A child can become satanic despite having good parents. A quick question "How does God feel about His stubborn former son a.k.a satan?"

Also, many people live in perpetual sadness because of the foolish decisions of their siblings or close friends. For example, you told your friend not to marry someone and he/she did, or you told them not to invest in a ponzi scheme but they did, and now they want to make your life miserable because of their madness and greed. Don't allow them to!
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There are other people who need us to be happy and upbeat and who value our advice and contributions.
God told Samuel "How long will you mourn over Saul's disobedience! Move on!" Samuel moved on and gave us the wonderful King David!
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We must learn to move on with our lives and be happy despite the pain the foolish decisions of loved ones bring about.
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May the Lord help us to overcome. In Jesus name! Amen!