The problem is that when infants are left to cry themselves to sleep, they are forced to conclude that they are not lovable enough to engage their parents' desires to comfort them. If they actually stop crying, it is because they have abandoned all hope that help will come.
Seriously? Have you ever been around a baby for more than an hour? Babies can't conclude. Beck isn't thinking, "I have deducted from my experience here in my crib that my parents just don't love me enough to bother." And the "abandon all hope" part was a little much as well. Don't worry, I'm not gonna just throw him in his crib and leave him there for as long as it takes to fall asleep, but I'm also not gonna go sing kumbaya with him.