Why is democracy not a magical tonic for all problems?

Democracy works slowly, and is not always very efficient at getting things done quickly. Take the failed Weimar Republic of Germany for example; after the first world war, the allies forced a democratic government upon Germany. The German people were used to having a strong leader, and after WW1 the country was left in economic ruin. A strong leader was needed to get things done and for this reason the Weimar Republic failed.