With this perk, you suffer no effects from Minor Radiation Poisoning (-1 END). This perk has no effect on greater radiation levels. For example, Advanced Radiation Poisoning (-2 END, -1 AGI) will still affect your character and so on. Unless your Endurance score is already at 10, using Intense Training to increase your Endurance would be more effective than taking this perk. Moreover, by this level the player will no doubt have multiple, plentiful ways of curing radiation sickness, and the Endurance loss has almost no effect on performance anyway (HP will not be reduced by the temporary condition, only poison resistance, itself a seldom-used statistic), so this perk is of dubious use, if any. In addition, the skill points lost at any radiation level can be restored (permanently) by reading skill books, since the game tracks points beyond 100 even though they aren't factored in normally.