If you're in public and you see a mother at a store with a screaming infant, like most people you may be tempted to come over to see what's going on. Perhaps you will go "awwwww, poor baby!" or "what's wrong little one?" or even speculate on what has the baby so upset. Before you do such a thing, take a step back for a moment. A baby's cry is designed to cause physical discomfort to those who are subjected to it. This is especially true in the case of the mother, though always to a higher degree.
If the baby is screaming, remember that inside the mother is as well.
She wants nothing more than to leave the store and go home because 9 times out of 10, a car ride makes the crying stop. Walking up to a crying baby is actually the worst thing you can possibly do because it delays the mother's departure and makes her feel even worse. The best thing you can possibly do is walk away. Bonus points for a sympathetic smile in the mother's direction. Please just leave it at that.
Because if I am surrounded by a bunch of strangers awwwing over my screaming baby and prevented from leaving a store ever again I am not going to hold in my scream for the privacy of my car.