Why do you think jack doesn't believe early about fisher

Much to Jack’s astonishment, Fisher was alive and they found him. He alone had survived the attack by German soldiers was traumatized by the incident. His squad had been taken out by the Germans. He had to deal with a physical injury he sustained and survivor guilt. Jack recruited his father, another military man, to convince Fisher that he can come home and recover from the devastation that he suffered in the war.