So I was gonna start this at the bugs section but maybe I'm not understanding this right.

Stealth Spidey synegy with IMIW says reduced shock and incinerate effect by 100%. What does that really mean for the game and matchups? I'm not quite clear. I fought Electro with Stealth and wasn't expecting the damage back from shock when I applied the slow debuff but I did. What does it mean effect of something? And when do I use this synergy. I'd appreciate any help.