Think of the best way to translate the proverb "The grass is always greener on the other side of the fence" Into Russia a short story to illustrate it.

Трава всегда зеленее за забором. (Хорошо там, где нас нет)
For example you come to the shop and want to buy an apple. You take one aplle, but then you see that another apple is bigger, you take that one and realise that the third one is even better then the second and so on.