Toughness/EHP is calculated as Life divided by your combined damage-reduction factor, which correctly predicts how much TOTAL incoming damage you can absorb over time, but does not by itself describe whether any SINGLE hit in that stream exceeds your current Life and kills you outright.
This explains a frequently-reported experience: a character with an impressive Toughness stat dies instantly to one attack in the Pit despite that same character comfortably surviving long, sustained fights against normal packs. The two scenarios stress completely different things - sustained average damage versus one single outlier hit - and Toughness only directly answers the first.
This is a synthesis of def_max_life_sets_the_oneshot_ceiling and the EHP formula already documented in this project's damage_model.json: EHP scales Life by a DR multiplier for AVERAGE damage calculations, but any hit whose raw damage exceeds your CURRENT actual Life (after DR is applied to that specific hit) still kills you, regardless of your average Toughness rating.
Do not treat a single Toughness number as sufficient defensive planning for content with known burst/one-shot mechanics (Pit bosses, certain Elite affixes); cross-check your raw Life pool specifically against the largest reported hits in that content.
defensiveLikelyAll
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