I think I know what you mean, Debbie. Sometime it just hits you as to what proportion is missing. Great if it saves an item you still like; I've recently had both "toss and move on " epiphanies and "oh, this is how I should wear that" epiphanies and rescued something from the toss pile. They're both fun as style gets more focused.
Usually the item has to fit well of itself, and be a good fabric (comfortable or easy-care or luxurious or color). As in, flattering in the right context. The ones I need to toss I can almost always finally pinpoint a fit issue--too short, too tight, something.