No, letting a baby cry doesn’t strengthen his lungs. You do not have to respond promptly to your baby’s cry. You should do your best to comfort the baby even though sometimes an overwhelmed baby may need to be left alone for a few minutes to fall asleep.
Babies cry because they need something even though sometimes it may be difficult to know exactly what they want. They cry because they are hungry, wet, tired or overstimulated. They may need to vent, suck or just be comforted. Sometimes babies have fussy periods when they are unconsolable. In this case crying may help them steam off. However crying doesn’t help babies physically or emotionally. It doesn’t teach them to cry less.