Anyone old enough to remember the Kenny Rogers song that went something like 'know when to hold 'em, when to fold 'em'? A very important photographic skill is to know when to walk away from an image, whether in the darkroom or in Photoshop. It really hurts to hit that close, button, then 'don'd save' but it often needs to be done.
I find that all too often an image which looked great standing there didn't in fact translate into a picture, for a variety of reasons (a topic for another time), or the picture has all the right elements, they just don't work together, or one element is missing or wrong and no matter how you try to disguise it, crop it, darken it to oblivion, it still spoils the image.
The temptation is to keep working on the image, deluding yourself into believing that if you play with it long enough, great art will ensue. My own experience is that I'm cutting my lossses earlier and earlier. I can always go back to the raw image and retry in the future - perhaps then I will see what it was that made me take the picture and make something of it, more likely I'll reject it again, but bottom line is I save myself two hours of wasted Photoshop work.
In general, if I'm not sure if an image is good - it isn't. Even if someone later comes across one of my test prints of the image in the garbage can and admires it, it still doesn't become a favourite image. Conclusion, throw it away, you're not going to miss it.