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.
2. It's about understandings towards life. Summer and Tom have totally different sets of life values. Summer followed her incentives , disbelieved in the existence of love, enjoyed the moments before, did what ever she wanted. Tom had faith in soulmate, ?fate, the one and issues etc. , blind to the truth, lost in fantasies. Ironically, long time after their ?"broke-up", both of them claimed that the other was right, as if they exchanged their life values. We may come to a conclusion that there is no true or false life understandings. Just different. And don't haste to judge.