to be honest, i didnt get a thing about this film ;(
but i gotta post something!!
well i got the part where the thing was lost, probably because it looked totally different from everything else. and at first, i thought that the thing was the boy himself, or i should say the boy was looking at the thing, and at the same time, he was also looking at himeself, because i thought the boy was also lost and felt lonely and didin't feel like he had a place to go home.
and as the boy grew older, he found what he wanted to do, and as soon as he found a place for himself, the boy probably felt like he found somewhere that made him feel like he belonged.
and so when the boy started feeling like he belonged somewhere, he couldn't see the thing anymore... because the thing was himself, and now that the boy isn't lost anymore, the thing isn't lost anymore too.
but i don't even know if the boy felt lonely and felt like he was lost in the first place so maybe my opinions might not make any sence, but thats what i thought after watching the film.