Honing My "Cry-dar"

Since becoming a mother, I've noticed I've developed a pretty good "cry radar" for other people's kids. Like, I'll see a frustrated mother scolding her little kid at the grocery store and think, "yo, Mom, your kid is clearly tired and unsure of the situation and probably just wants a little compassion or a hug or something. Can you just stop for a minute and empathize with him?"

Why is it that when I hear some other mom's kid cry, I immediately know what the problem is, and have an instant solution?

I wish I could emotionally detach enough to have that same kind of insight with my own kids sometimes.