I often find UFOs at the thrift stores and I will say, there is usually a reason on why it didn't get finished. Some of which is pretty obvious, some we just never know.
I have a perfectly nice top that was intended as a wedding gift for my husband's niece-equivalent (daughter of best friend). But... a lot of things happened and the wedding was called off and now I call it the "Jerry Springer Quilt".
I've taken apart badly made projects just for the fabric. If the pieces are big enough, I'll just cut them apart.
Sometimes I will rework a project, like there was this huge pink blobish thing that when I took the blocks apart and added sashing made a nice pair of twin sized quilts. Turns out those were heart blocks under those blobs.
The thing is, I know the feeling of "all that work and this is what I have to show for it" on my own failures. By this point in my quilting career I avoid most outright failures but still, sometimes things just don't go together like we see in our heads. Anyway, after putting in "all that work" myself, sometimes I'm not willing to put it right. But, thing is, with the thrift store UFOs, I didn't put in "all that work" to start with, I just see -- well hey, I can do this and that and have a reasonable project out of it.