Pseudocode for stealing and picking pockets is outlined below. The code indicates there is always a chance of failure, regardless of the skill of the creature performing the action.

        pick pockets:
          r = rand(1,100)
          if (r == 100) pp_fail()
          diff = actor->mod_pp_skill - target->mod_pp_skill
          if (r >= diff) pp_fail()
          if (target->mod_pp_skill == 255) pp_fail()
      
      steal in store:
          if ((actor->mod_pp_skill < store_steal_rate)
           or (store_steal_rate == 100))
              diff = 0
          else
              diff = actor->mod_pp_skill - store_steal_rate
          r = rand(1,100)
          if (r > diff) steal_fail()