This is exactly what a great psychological thriller should be. A film with a riveting twist that gives the viewer a mental/emotional/psychological sense of whiplash right at the moment of the twist reveal. Secret Window was the same way with me, as was The Sixth Sense also (just to name a few).

I didn't get it the first time around. I had to watch it again and again. I've now seen it collectively around 4 or 5 times. It hasn't really gotten old yet. But there are still some unanswered questions I have.

And while I've read some helpful articles on the topic of interpreting this film online, I'll probably still need to watch it again.