"If we are not our brother's keeper, at least let us not be his executioner"

This quote by Marlon Brando highlights the importance of keeping an eye out for one another and not triggering damage to others. It recommends that even if we are not actively helping or supporting our fellow humans, we need to a minimum of refrain from triggering them damage or being the cause of their failure. The phrase "sibling's keeper" refers to the scriptural story of Cain and Abel, where Cain asks God if he is his bro's keeper after he has killed him. Brando's quote advises us that we have an obligation to each other as human beings and need to not add to each other's suffering.