This achievement is unlocked by completing the personal mission on a character with the "Weak" trait. This trait makes your character unable to use melee weapons of any kind, this includes throwing them since you cannot equip the weapons in the first place. The personal mission can still be attained normally through the use of firearms instead of melee weapons. Once the funds for your personal mission are earned, speak to Sader Fiasco to gain access to your personal mission. Complete the mission. Achievement Unlocked.