At the very beginning, the director told us the theme of this film.
It's a story of a boy likes a girl, but it's not a story of love.
Then what's it about? It seems like the director just led us to a crossroad, but did't tell us which direction to go, except "Love is a wrong direction".
A-thousand-Hamlets thing. Here's just two from my view.
1. It's about feelings and facts. Tom built up all the romances in his mind, but he didn't even notice the simplest truth that Summer never ever admit their relationship. Firstly, the truth seems coincided with the picture in his mind. Then, the truth diverged with his expectations. And he collapsed. Shall we call it a tragedy of characteristics? Which's shared by many fantasts, count me in, perhaps.
And Children Know EVERYTHING.