A person A negotiating with a person B the purchase of a product, has several issues to negotiate such as price, quality and scope of work.
This person A has several positions with respect to different issues, for example for the price he has the position of 100 pesos for the quality he has a standard established as a position, but the interest behind each position is the reason for the position.
In the case of the price, the position of 100 pesos is such, perhaps because the person has an interest in completing with his budget the tuition of his children plus the purchase of the product that person B is selling him.
If we know the interests of the parties we can come to negotiate satisfying the needs of both A and B.
Negotiation is a continuous dance of interests with positions like shells that obscure them. The key to successful negotiation is to discover behind those shells the interests of both in the different issues to be negotiated.
When we are in full negotiation we must carefully evaluate what impact our decision-making on this or that matter will have on the interests of the person with whom we are negotiating. The key is to know what the interests of both are and what is their hierarchical order; in such a way that we mentally make a balance of decision-making and impact on interest.
By doing these mental balances we will arrive at several options that we can offer to the other party.
There will be options where the balance of interest impacts is more positive than others. The best alternative to non-agreement will be one where the balance of interest impacts is negative for any party.
The idea is that we negotiate the interests of both parties and not the positions and in this way we will reach a favorable situation for both.
