Rusting old tanker

You're right - continuing to fight with a painting when you've just lost all your passion for it is just getting in the way of trying something else: it's something that probably happens to us all.  I have laboured over paintings - most particularly acrylics, which at least lend themselves to layering and glazing - for days and even weeks on end; I've often been as happy with the end result as I ever am, and it was worth all the work.  With others though - what happens now and then is just that one really loses so much interest that one also becomes desperate, slapping the paint on in the hope that SOMETHING will emerge from it.  This is invariably a bad idea and a good way of wasting time.  Some things just aren't going to work, nor is it easy to discover the basic reason - could be a weak fundamental drawing, composition that's just "off" in ways you can't define, could be the medium you chose isn't the one best suited to the subject: and any number of other possibilities.   But if putting it away for a month or so and then giving it a hard state isn't working, or you realize it's just failed, then flogging on with it is far less satisfying than putting your boot through it.  If your painting were mine, I'd make that large shape on the left a lot darker, to push your rusty old tanker forwards a bit, because there's not enough tonal contrast as it stands: but one simple step is rarely the right answer, you'd have to re-adjust all over the painting in consequence, and if you feel "sod that for a game of soldiers" - I'm sure we'll all sympathize.