In fiction, a foil is a character who contrasts with another character (usually the protagonist) in order to highlight particular qualities of the other character.[2][3][4] In some cases, a subplot can be used as a foil to the main plot. This is especially true in the case of metafiction and the "story within a story" motif.[5] The word foil comes from the old practice of backing gems with foil in order to make them shine more brightly.[6]

The idea of foil from literature is one that has helped me to shape my own desires in a LTR. I wanted to share. This idea with you all and see if you agree that this is the best possible dynamic to have in a marriage or LTR. The idea of being close with someone you love so as to almost live vicariously through that other person. To experience life through their eyes and point of view, elevating your own. What do you think?

The protagonist is relative to each of you, since we all live in our own lives, just wanted to make that clear.