The line between failure and success is so fine that what seems hopeless failure may turn to success.

glorious（輝煌的、光榮的）與前文 hopeless failure（絕望的失敗）形成鮮明對比，glorious success（輝煌的成功）為自然的英文搭配，完全符合「失敗與成功僅一線之隔」的語意，故為正解。