How can a doctor tell if you're healthy by listening to you breathe through a stethoscope?

Auscultation : Physicians listen to a patients lungs to ensure their breath sounds are clear. Physicians can hear wheezing, crackles, decreased breath sounds and start to diagnose things like pneumonia, COPD, Congestive Heart Failure, and other conditions such as pneumothorax, etc. A doctor may even employ egophany or whispered pectoriloquy. Auscultation is a powerful tool to examine people.

1 part of puzzle.: While a doctor can learn a lot about your health through listening to you breathe with a stethoscope, it by no means alone that you are healthy. To know that you are truly healthy would require a complete examination, medical history , evaluation of health habits and lifestyle choices, blood testing, preventive health measures. There's a lot behind using the term "healthy".