[visarga]

Trying to predict desire might be easy, but predicting happiness in a relationship hard. It's like a weather simulation after the first 10 days - becomes too hard to compute.

Besides attraction, other things might come into play in predicting relation happiness - such as dialogue style, extraversion/introversion, specific needs of one in relation to the strengths of the other and specific situations in life the couple has to deal with. Some of these things might emerge from a psychological interview, others happen dynamically and are impossible to predict.

And most people are very time sensitive - the same person might be available now that was not a week ago. The availability for dating of some people measures in just months between long term relationships, so they are like 99% of the time unavailable even if they are compatible. Searching for a mate is hard because most compatible people are presently attached and you got to get them at the right time. That might be mitigated by going on a dating site, but unfortunately dating sites are full of people who are there for other reasons than serious relationships.