If infants know they should fall on their tummy three months after birth, and to crawl in their sixth month and to walk in their twelfth month without anyone telling them, why don’t they also learn beforehand (who teaches them, anyway?) that glass would break if they drop it, they would hurt themselves if they fall, and all the remaining basic lessons of human existence, without their having to experience each to understand, or poor harassed mothers screaming at them at every juncture?