If the addressed person cannot withdraw from the situation, that person cannot decide which message is real and may develop pathologies. If the addressed person cannot decide which message is accurate, that person may withdraw from the relationship. People in such relationships may be unable to fulfill each other's wishes, and miss opportunities to express love.
Double Wishes come in various flavors.
I want X and Y . I cannot have X and Y simultaneously. I want you to decide if I should X first or Y first. I want X so that Y. I want Y but X is the only way to get it. I wish I could X .