The message in 500 Days of Summer is that people who over romanticize their relationships tend to miss subtle hints that their partner isn’t happy, so they are taken by surprise when it doesn’t work out, but Tumblr as a whole seems to think that it’s just about wallowing in self pity after a break up and “oh my god this movie is my life” because they all feel sorry for Tom because Summer was a bitch who broke his heart, and Autumn and Tom are the perfect “otp”