@Ganymede said:
This presumes that one is "fit," and that maintenance is the goal. For many, it's not.
I'm in no way an expert and on top of it I'm not a doctor, so this will be likely different for people dealing with different health issues.
However a few years ago I found myself in my early 30s, overweight and completely out of shape. I wasn't used to that, it sort of snuck up on me since I always used to play basketball, I walked everywhere, loved hiking, etc. But my lower back was suddenly giving up on me and even half-court ball with 25-year olds was killing me.
I found relatively non-critical adjustments to my diet and exercise helped a ton. I mean I went cold turkey on Coke, stopped eating obvious bad things like cookies, and replaced fries/rice with salads. Basically my diet was pretty much described as "meat with salad", and I'm not talking small helpings either. Lots of it. I went to the gym three times a week and lifted, 30-40 minutes a session tops.
I lost 50ish pounds in half a year. It does work. It doesn't even take huge sacrifices, it takes small ones on a daily basis. So I wasn't on maintenance - that's empirical though, it's what worked for me, and it might be different for other people.
Either way those small sacrifices, compounded by life and other obligations are still hard. Christmas? Try eating right around Christmas when there are sweets everywhere, right? Willpower is a muscle and like every muscle if you overwork it, it'll get tired and fail. Plus as mentioned above those 30-40 minutes hurt when you're on a rather limited time budget to begin with. But it's doable, for sure.
I think the best trick is to figure out some motivation even if you have to invent it. Be competitive with someone if you've got a competitive nature, or be part of a group to get peer pressure to work in your favor or... something. It's a personal thing obviously.