The idiom is very important as it shows us a part of humans psichology. It is about jealousy. It happems in our days that eventhough two people may have exatly the same thing they think that the other one has the better one. Think of two gardens , one belong to a person and the second to his neighbour. Eventhough they have the same each of the wants to havethe better one, so their minds create the illusion that the neighbour has the better one
just as a metter of fact it is true that it is true that it looks greener(light comes in a smaller angle)
