The thing is every single dieter goes through this op. That's why people fall off the wagon constantly.
Diets by their nature are restrictive, after you've done them for a period, be it a day, a month, or a year, people just want to go back to their old ways and enjoy the things they used to. It just seems a bit shit to have to continue.
A stone is on one hand a lot of weight, on the other hardly any and can be regained in a couple of weeks if you proper let yourself go.
For me what works is the thought of undoing all the hard work. Of failing. If you think of the summer time, do you want to be there another couple of stone down, maybe even at your target weight, or looking back and thinking Youre the same size or bigger as you were when you started.
Can you visualise what made you start the diet? What was it, how you would look? The clothes you could wear? How comfy you'd be in the heat? Healthy benefits?
For me it's pure vanity, I've been overweight a few times in my life, and I hate that sweaty trying on of stuff, wondering what makes me look less fat, I love being able to put anything I want on and thinking I look ok.
I do keto and the gym, we all have different things that work for us, but whenever I think of laying on the sofa with a tub of Ben and Jerry's, I think about going back to being uncomfortable, not liking my appearance, and that's what gets me motivated.