Incrementalism and mindless snacks are the worst enemies.
We went on a 2-week Viking river cruise in Europe. I didn’t realize until the 10th day that I was eating larger portions — no extra snacks. I cut back, but it was too late. I gained 10 pounds and it took 8 months at my normal food level to lose them.
I tried ice cream at home, starting with a small portion occasionally with fruit. That would have been ok, but a month later, I was eating twice as much with almost every lunch and dinner.
We don’t keep snacks in the house, eat reasonable sized meals, and always split a plate at restaurants. Their portions are insane. For example, one large McDonald’s hamburger sandwich now has more calories than 6 regular hamburgers when I was in high school.
You have to be diligent all of the time.