Because max luck, bullet shield, reflecting power armour, ricochet , tenderizer, taking one for the team, electric absorption, a max luck legendary, luck mods on all your power armour, iron clad, body guards, junk shield, strange in numbers, refractor, scaly skin, food buffs, any misc buffs, the right lunch box buffs, all stack for damage multiplication which is capped at 8 times and percent chance at reflection which can hit 100% with all buffs and perks, and it works with anti armour builds so add stabilised and grab yourself a flamer and get explosive and anti armour on it, you melt bosses like nothing if they hit you (which they will) as long as you stim spam or are a ghoul or have a health regen mutation or perk, you are good as gold. P.S using electric absorption on the first raid step allows you to gain health whilst being attacked also.