is how 2 weeks of eating well can be entirely undone by 2 days of eating poorly.
It makes it all seem pointless.
Other things aren't like this. Practicing a musical instrument consistently for two weeks isn't a waste if you skip two days. Going 2 days without reading doesn't negate all you've learned from two weeks of reading daily. Being a great mom for two weeks straight (have I ever managed that long of an unbroken stretch? doubtful) isn't destroyed by two days of hiding in your room eating ice cream while the kids watch tv all day.
Yum...ice cream. Great. Now I'm hungry.
It's not fair. I'm totally over here pouting.
But I'm not eating the ice cream.