I think most people didn't get it cause it's a deep thinker and it doesn't tell you straight out what happening.
I didn't watch this movie all at once. Took me about 3 days because I get distracted easily. I did cry when she gave the unicorn away. I kept thinking that they would show her talking to thin air like the crazy person she is, but no. Instead they pass the delusion on to her boyfriend and now they both look insane. To be honest, I think she's schizophrenic.
I feel really bad for her parents. They sheltered her from the real world and she grew up with an unusual imagination. However, I don't think that's her downfall, rather it's her creativity and artistic talent that makes her unique. Her drawings were amazing. She was a true artist.
Her failure stems from her inability to face reality. She's in super denial of what's real and what's fantasy. Like a person believing in Santa Clause all the way into their adulthood and they very idea that what shes believes is not real is heartbreaking to watch. Again, symptoms of schizophrenia which perhaps is not her parents fault. She's just insane.
Her failures should have "woken her up" to reality, but instead that damn unicorn store got her messed up. And her parents do exactly what they shouldn't do. They give her that unconditional love she's addicted to, and tell her everything is ok, even when it's not. They lie to her instead of getting her help. That part was even more sad to watch. In the end, I think she has a mental disease. Nothing bright, pink or rosy will flourish from her life. She won't accomplish anything. It's sad. Good movie.