And the LORD said unto Cain, Why art thou wroth? and why is thy countenance fallen? If thou doest well, shalt thou not be accepted? and if thou doest not well, sin lieth at the door. And unto thee shall be his desire, and thou shalt rule over him. And Cain talked with Abel his brother: and it came to pass, when they were in the field, that Cain rose up against Abel his brother, and slew him.
The first appearance of a man experiencing rejection in the Bible was in Genesis 3. When the eyes of the couple were opened, they knew that they were naked. They knew that the state that they were in was insufficient, and they suffered shame. This was the first rejection.
Shortly after, their son Cain experienced similar rejection. His offering was not accepted as a way to seek God, and so he was angry and his face downcast.
In both of these cases, the conditions of the rejection were the men’s relationship with God. In the first, the man lost his fellowship with God, in the second, the other man failed to regain it through an inappropriate offering.