To me compatibility is having the same core beliefs, but not necessarily the same personalities. Often outgoing personalities will successfully link up with introvert personalities, but someone with radical right wing political views is unlikely to be compatible with someone with radical left-wing views. In some ways my OH of 24 years is very different,has some hobbies and interests that just don't interest me and visa versa, but we both agree and support the right to do things on our own. Most of the time when we become 'incompatible' it is due to previous experiences one of us has not had, and the inability of the other person to cut some slack or understand how that has impacted on our personality. I don't think sexual chemistry has anything to do with it,that comes with pracatice ;-)