Subjectivity in Evaluations of Crap in Writing

You know that feeling you get when you’re reading an old manuscript and you think—“this is crap! Why did I not know this was crap when I was writing it?”
And you know that feeling you get when you’re reading a different old manuscript and you think—“this is amazing! Why didn’t I finish writing this? I love this”—and you start working on it again.
(This is related to the feeling you sometimes get when reading galleys or sometimes printed books and you have what is almost an out-of-body experience where you don’t remember writing this, but it’s so good and you think you might be in love with the writer, only that’s weird to say since it’s yourself.)
Have you ever had the experience where a manuscript you reread and thought was crap is suddenly transformed into the manuscript of brilliance? Or the reverse?
I do not know what causes this. It probably just means that I’m having a bad day or a good day. But when you are this subjectively swayed by the quality of your own work, it’s a good time to sit down and realize that hating a novel written by someone else or loving it—it’s all equally subjective. You found those books on the wrong day—or the right day. You read them at the right age—or the wrong age.
It has nothing to do with the book. It’s you.
Except, of course, when it’s your book. Then when you think it’s crap, it really is crap.