To me, negative effects of the spell are like reagents. The only reason a spell costs what it does is because the reagents are used up. So in that sense, the spell is being fueled by the discard.Overload is not directly related to the mana cost - you're creating that association. The best way we can see Overload falling over, the way that you describe (to use the same criticism as 'if you have no cards to discard' is if you coin out two Dust Devils on turn 1. You are hit with Overload: 4, but you can only pay 2 mana in overload costs the following turn. You don't also lose two more mana on turn 3. So by your argument, since you have insufficient mana to overload, is it not just an effect of the casting?Think about how your mana is stored - in crystals. The side effect of casting a spell is that one of your crystals fizzes out for a turn - think of it like a power surge that knocks out some of your ability to access your rooftop solar panels. It's not that it spends the mana next turn (otherwise, how would we get it back when we cast things like Lava Shock? We're not gaining mana, Innervate style, but we're restoring locked mana crystals.), but that your mana is unavailable.Edit: On a side note, I've not actually played Shaman enough to know what happens if a Lightning Bolt is counterspelled. Do you still incur the overload?