I think romantic compatibility runs on the same three realms as the rest of life: the physical, the emotional, and the intellectual. A lasting match needs fit in all three, though not a perfect one. In love, fit in each realm is a matter of taste and feeling. Robert Sternberg’s triangular theory, the best-known model of love, also has three parts: intimacy, passion, and commitment. It leaves out the intellect, and it leaves out luck.
The order of the realms matters a little too. Partners who rank the realms the same way may get along more easily. The similarity evidence says not to lean on that. A meta-analysis of 313 studies found that actual similarity stopped predicting attraction once people were in a relationship. Perceived similarity still predicted it.
The fourth factor is serendipity, the luck that brings two people together. It is not a realm, because it is not something a mind does. The three realms describe the fit, but luck decides whether two people meet at all, and when. Plain nearness shapes who pairs up, which psychologists call the propinquity effect. Fit is also hard to foresee. In a 2017 speed-dating study, over 100 measures of traits and preferences could not predict which specific pairs would want each other.
So I see the three realms as the part of compatibility we can judge once we meet, and luck as the part we cannot. Luck is partly built, as Personal Growth argues. It still gets a vote.