1. You don’t have a gun.
2. You cannot easily accesses your gun because of clothing or position. (concealed carry, fallen or against a wall)
3. The average attack occurs in less than 2.5 seconds. (21-foot rule)
4. The average human mental reaction time is nearly one second.
5. The average draw to presentation from an open holster takes over 2.5 seconds.
Read more about why a gun doesn't always beat a knife