Did you ever try to put a broken piece of glass back together? Even if the pieces fit, you can't make it whole again the way it was. But if you're clever, you can still use the pieces to make other useful things. Maybe even something wonderful, like a mosaic.
Well, plans are a lot like glass. When they don't work out, people try to put them back together like they were, instead of trying to use what's left to make something that's better.