Why did the doctor believe that johnsy's desire to live was important?

The doctor believed that Johnsy's desire to live was crucial because it played a significant role in her recovery from pneumonia. He understood that a strong will to live could positively influence her physical health and resilience against the illness. Without that motivation, her chances of recovery diminished, highlighting the connection between mental and physical well-being. By fostering hope and encouraging her to fight for her life, he aimed to instill a sense of purpose that could aid in her healing process.