The phrase "be the mark" indicates achieving a target or goal, but there are several antonyms that denote the opposite. The first antonym is "miss the mark," which means failing to meet the target or goal. The second antonym is "fall short," which refers to not achieving the expected outcome. Another antonym is "come up short," which implies that efforts were not enough to achieve the desired results. "Grossly overestimate" is another the antonym that signifies exaggerating abilities or competencies, which are not commensurate with the target. Finally, "underachieve" refers to failing to meet the requirement for success. These antonyms highlight the different ways one can fail to "be the mark.