Not just personal unhappiness but all strife in life, including war, is the result of an over-emphasis on temporary things; money, power and material possession.
Books are fountains of knowledge and also help the heart find the way to use that knowledge with wisdom.
All that happens in our lives which we find painful, physically or emotionally, is for a purpose. Unfortunately, from our very limited perspective it is often not possible to see the good in it. The divine plan is not available to our eyes.