Sugar is amazingly addicting. I (mostly) went off sugar in April, and with a few slip-ups and self-granted exceptions, I've been (mostly) off it ever since.
Sundays are my exception days, and every Monday my addiction is back in force. It is amazingly physical, this need for sugar. Fruit does not suffice. The one thing that will trick my brain into thinking it has had sweet without actually ingesting any sweet is flavored sparkling water. Every Monday, it is only sheer force of will that gets me back on the no-sugar bandwagon.
It isn't sugar, really, the problem. It is Red 40 and high fructose corn syrup and no one needs daily sour Jelly Bellies. They just don't. I just don't.
I read somewhere recently that sugar is like a drug not only in the addiction factor, but that you need more and more of it to get the same high. I can see that. I can feel it, even, on Sundays, but it doesn't stop my feast-or-famine primitive brain from cramming all the sugar it can many Sundays. Which is better than cramming all the sugar it can every day of the week.