I think it's just the most "natural" attraction you can experience but by the same token you'll still feel a stronger attraction to someone you share (positive) memories with than a dual by simple proxy of them being your dual. in the case of your dual, it may just be that it takes less time for the two of you to find common ground, communicate, and build and maintain a relationship because you share similar preferences/expectations. I don't know if it's a myth per se but I think there's at least a semblance of validity to the idea that there's a subset of people out there that you're naturally more compatible with than the rest of the population. with that said, don't think about it too much. just be yourself, like whoever you like, and let fate take care of the rest.