The lost domain.

A few days ago I saw a dead cat on the road, its face smashed in, and I felt... nothing. Well, a momentary flicker of pity, and some revulsion. By contrast - and I don't mean to sentimentalise - I remember finding a squashed hedgehog as a boy, and being inconsolable. That openness of heart represents, for me, the lost domain of childhood; perhaps it is also what the mysterious estate was for Le Grand Meaulnes, or the special summer session for Gene and Phineas in A Separate Peace. Why do we have to lose that openness, and can it be regained?