Joseph's murderous brothers unknowingly helped his dreams come true. They had helped lift their little brother toward his exalted calling without knowing it. Had Joseph fully known each detail of his future he would have withdrawn from it in fear. I think the if we knew our whole life in front of us, we probably wouldn't be able to face it. If you knew that divorce was coming, that death.
Humans can only handle one day at a time.
All Joseph had to do was follow God's will for one day. Joseph was there on a Divine mission. Psalms says he was SENT of God to do God's work. His slavery was no accident. We're just like Joseph.