The covet thing I kind of catagorize as more of "You want (more) what you can't have", which also feeds into the idea you mentioned about "rank".

There is a theory that the more you have to work for something, the more valuable it is to you, which would make sense why some relationships which start off as one-night stands tend to remain so whereas after investing a lot of "get to know you" time, the relationship may last longer. There are always exceptions, but no one likes to feel as they've wasted time, energy, or money.