The cows wouldn't be straining their necks against the barbed wire if there was plentiful long green grass on their own side of the fence.
"Ah, the grass is always greener on the other side of the fence, me lad." I always imagine it being said by a strict Scottish Presbyterian uncle. His meaning is clear: "Be content with your lot in life, and change not your course."
Which is hogwash. Or, cattle droppings, lest we mix metaphors to excess.
The reason the grass on the other side of the fence looks better to the cows is that they never looked over there, until the grass on their own side ran low. It's a cognitive dissonance thing. You don't look for something better until your current something good seems to have become something less.
Personal example. I run on fire trails. The vehicles that move over these dirt roads make the familiar double ruts through grassy loam, hard cracked adobe, or broken sandstone. A runner (or cyclist or equestrian) chooses his rut and travels in it. Until the rut you're in starts to afford some tricky footing, you don't even think about the rut you're in. But when you realize you're in a rough rut, you look over at the other side of the road ... Mirabile dictu! The
It seems that way, not because it merely appears (falsely), but because it really is -- because it was not examined until you needed to examine it.
I leave the finding of a moral to this story as an exercise for the reader. Or just ask the Duchess.