Vayeshev :Why are dreams prophetic? 

Speech, including the way we express ideas to ourselves, is  a  highly edited product. The path from the motive to the action goes through  numerous filters.  Some are conscious, others can be realized on reflection; (probably) most are obscure. Dreams have a different set of editors, maybe some of the proofreaders are asleep. Seeing thoughts and motivations in this divergent form is revealing.  The personal reality of the dreamer is told as a novel instead of a news article; there are embellishments and revelations. 

Joseph is designated as the legacy of Jacob. This is a shocking statement of favoritism. That selection is reflected in  his appointment as  supervisor of  his brothers. In his dream Joseph imagines himself the monarch to whom all his siblings - and even his parents- bow to. Is this not just another, novelistic, version of his  reality? Did not  the other brothers have similar dreams of dominance? 

Certainly Reuben wanted to lead the family. He was the first born... if you count the children of Leah ( the wife that was married accidently). When the subsequently-born brothers plot to kill Joseph, Reuben convinces them to throw him into a pit and secretly plots to return and rescue the Joseph.  Reuben would thereby gain the graces of his father Jacob … and betray his other brothers. But his plot dissolves and his road to the ascendancy of his dreams comes to naught.  Reuben expresses his anguish when Joseph is gone, revealing his duplicitous ambition. Is this the origin of the separation of the tribes with Reuben and Gad in trans-Jordan when the states are apportioned? 

Judah is the master of negotiation. He convinces the brothers to sell Joseph, rather than kill him. Selling your brother is a heinous crime, and, in Torah law, a capital offence, but the outcome is a living Joseph. Selling Joseph seems to cancel his dream.  Joseph will be a slave until he dies from overwork. Joseph's ascent through talent and Divine intervention is a model; it is a legacy of Jacob. Judah, who is the forbearer of the kings of Israel, will negotiate again with Joseph.  Then Judah will sell himself  into slavery to rescue Benjamin. 

The contrast between Joseph and Judah is staged. Judah leaves this family -  brothers that will kill one another, betray each other, sell a sibling.  He befriends an Adulamite and marries a local. Two sons die, the second, Onan, dies by Divine decree because  he will not sire a child who will not  have his full loyalty. His child, with the widow of his brother, will carry some part of the spirit of his dead brother; and Onan will not have that. The widow, Tamar, will not be left out of this genealogy. She  demeans herself, risks her life, plays the prostitute, to bear Judean offspring. Judah, as the stiffing John  contrasts with Joseph avoiding the advances of his master's wife. 

Joseph needs to go to prison. It makes the story better ( and every story has a dreamlike quality). He goes from a  pit to a pit within a pit. His clever interpretation of dreams, three days before the pharaoh's birthday [when the Pharaoh reviews his ministers' actions], establishes his power to see ( or make) reality from dreams.  The ascent of the [confident] wine steward and the beheading of the [terrified] baker create a lasting impression upon the survivor that is not erased, despite his efforts. 

Truth comes in many disguises. The alt-edited dream benefits from a clever interpreter.