Here's some simple, but striking truth about synastry (the comparison of two charts):

• Look for Person Number One's most noticeable major planetary configuration in their birth chart - such as a Tsquare, Stellium, Grand Trine, Yod, etc.
• Then look to see if Person Number Two has a birth chart planet conjuncting one of the planets involved in Person Number One's planetary configuration (or maybe even a planet "completing" a major planetary configuration for Person Number One).
• Now reverse the procedure.

Now, that's often electric (compulsive) attraction! And it's (in my estimation) specifically one of the things that Dr Carl G Jung was referring to when concluding there is a case by case astrological connection between the individual needs (complexes) of one person and who that person ends up falling in love with...