Killing Goliath was one of the gravest mistakes David made as a young man. It led him into several unnecessary battles.
This book looks into why it took so long for David to get enthroned after his ordination. The mistake he made was that he killed Goliath who was raised to kill Saul and end his reign. This led to the struggles of David and the horrible experiences he had en-route the throne. He repeated the mistake later in life but this time around, he avoided a battle he should have fought. This again brought him battles unwarranted. The book actually is a way of showing the real man in the saintly David we all like to think of.