So, can you see it?
There is one rotated half-square triangle unit in this quilt. I sewed the blocks, pressed them, and squared them up. Didn't notice it. I arranged them on my design wall and stared at them off and on for at least a week while I auditioned several different colors of sashing and worked out the border design. Didn't notice it. I sewed it together, pressed the entire top, spread it out on the floor and crawled all over it, basting it with safety pins, and then took a photo of the quilt. Didn't notice it. I spent several hours machine quilting the quilt. Didn't notice it. I spread it out on the floor again and buried the quilting thread tails and carefully pinned the binding to the front of the quilt. Didn't notice it. Not until I hand-sewed a quarter of the binding to the back of the quilt and spread it out on the floor again to check that I wasn't getting any border wave did I see the one rotated half-square triangle unit.
I am not fixing it.