Why didn’t Beah’s uncle believe he was going to the United States?

He doesn't believe that Beah has the fortitude and courage to go. Throughout the arduous preparation to leave, Beah’s uncle jokingly warns Beah again not to get his hopes up. Even on the day Beah departs for the airport to fly to the U.S., his uncle and the rest of his new family laugh and joke that he will only be “late for dinner.”