When we were paying off our debts we went bonkers occasionally. It culminated in the Scotch Egg incident - I discovered a Scotch Egg wrapper in the car, DH had had a deprived moment, impulse bought the item and ate it secretly hoping I'd never find out. It was a watershed moment for us weirdly. I took it to heart thinking I wasn't feeding us well enough and DH felt guilty because he'd "wasted" a quid.
Of course it was neither of those things, it was just a spur of the moment thing to release a bit of pressure after months of having no frills.
So we added a release valve. We shared a Twix (well, Lidl's version) in the evening. It was amazing, cost less than a quid a week, we didn't have one every night but it was good to have a little treat and a little choice. Yes I could have baked a cake but this was the point, it was a break from doing everything ourselves. It was just a daft thing "just because" and it kept us on track. We did a lot of telling ourselves "no" during that period, but sometimes a little sweetness helped to keep us working.
It's different when you're frugal through choice. When you've set a goal and you're going for it I think it's easier to say no to yourself because when it comes down to it, you have options. You could ease up for a month and buy that whatever-it-is you want/need. It almost certainly wouldn't happen because you know that £100 spent now wouldn't be as pleasing as leaving that money to do what it needs to do to work towards your goal. But it's a choice. When there's no spare cash because there just isn't the psychology is different.
Now we are kind of frugal by choice but we still have our safety valve. We have £10 a week to spend as we wish. That's £10 between us, not £10 each, what craziness would that be? It's a great amount for us, just enough to keep us pushing to save more but knowing we have a little wiggle room. Again, we don't spend it every week and when we don't it goes into the change jar. But it means we can have a paper if we choose - sometimes it's nice to have a real paper not just to read online. It pays for any books we've reserved at the library (they cost 60p), we might get a cuppa when we're out, or a couple of drinks at the pub, or a bag of chips, or an eyeshadow for me or something from the charity shop or a couple of music downloads. There's a lot you can get for a tenner. It's cheap and cheerful and makes us appreciate living now, not just saving for the future.
I know some folk would disagree and tell us to act like grown ups and tell ourselves "no". If we reach a point where we have no income or need to really save that extra each week then we will. But at the minute things are good so we're choosing to live well. A tenner a week gives us choices and that's a good thing.