The phrase is the title of the 16th episode of Fear the Walking Dead (Season 4 finale), which originally aired on September 30, 2018. Episode Overview
For a deeper look into the events and character arcs of this season finale, you can watch this review: Episode 16: ... I Lose Myself
Morgan finds Martha, who has been bitten by a walker. She attempts to force him to kill her to prove that he is "weak," but he eventually kills her reanimated self after she dies from infection. The phrase is the title of the 16th