Something happens after the third day “off the wagon.”
The links between the chain of habits, especially when it’s a new one, stretches past breaking point.
It’s no longer a cheat day or a recovery weekend or whatever you want to call it to justify it at the time.
After three days, the old habits ambush the new ones, and generally they win.
One day is ok. Three days is pushing the limit.
On the fourth, it takes exponentially more energy to get back on the wagon. It’s travelled too far since we took a tumble.
It’s not impossible but you’ll have to work pretty hard to catch it up.