Duality is considered to be the best relations in socionika as it is a relation of the full complement. The two in a Dual relationship are like two parts of one unit. This is a kind of relationship when both partners are able to provide one another with exactly the support needed and able to protect the "Vulnerable" function of one another. All that comes naturally and effortless just by being exactly who you are.
The duals are always on different poles of logic - ethics, intuition - sensorics and extrovertion - introversion dichotomies and on the same pole of rational - irrational dichotomy. In Dual relations, both partners are always from the same Quadra and therefore share the same Values.
The aspects in the strongest conscious functions ( the "Ego" block) of one partner will be the aspects of the accepting block of the other partner and vice versa, so they provide each other with exactly what is needed.
They are also almost to disturb one another's "Refusing" block, as the aspects of it are linked with the Subconscious (therefore not verbalizing) block of the other partner.
In Dual relationships the problems are solved a lot more easily and arise more rarely than in any other relationships as the partners share the attitudes and have a natural way of protecting the weakest spots and not judging the flaws of the other partner. In fact, what might be perceived by external observers as a disadvantage of a person or even a cruel behaviour, will go unnoticed or seen as a charming feature of a character by his Dual.
The hardest bit in the Dual relations is the first stage - how the Duals meet and make the first contact and how the psychological distance becomes smaller. There are several reasons for that. First is that the Dual doesn't have much strength in the area of the others partners greatest confidence and knowledge so they might seem simple, not exciting enough to one another, comparing to the people of the same type ( "Identical Relationships"). This is more common for the introverts. On the other hand the extroverts often simply do not notice their quieter Duals, tending to get into the relationships with other extroverts.
Another reason is that there might not be enough trust and understanding in the beginning ( due to the huge differences in the perception of the world - the "Leading" function), especially if both partners didn't have previous experience of Dual relations.
The Dual relations are best for the romantic relationships in a long term. Partners develop a natural understanding of each other and take care of the different areas of life for each other. They have similar attitudes due to the shared values.
But being in the relationships with the Dual means to love a person, who, 'though shares the same attitudes, is quite different. Sometimes Duals naturally attract each other, and even people who never met Duals, describe the image of their future partner as one. In this case the image of the Dual is attractive even in fiction (e.g. books or movies).
But it isn't rare also when people are looking for someone who resembles themselves more. In this case Duals seem too simple (as people are looking for the qualities that are strong in them).
Also sometimes people are looking for some of the qualities of their Dual, not paying much attention to the slight mismatch and end up with a partner of different type than their Dual, subconsciously expecting him to behave as a Dual.