Perhaps using Shock was a bad example on my part or else you're using it as a bad comparison. Although I can't think of any offhand, I'm sure there are burn spells that might sit in your hand useless on occasion (Thunderbolt maybe? I don't know...) So comparing them with your example of useless counterspells might be better. Perhaps Mana Leak would be a better comparison with Shock. After all, you're not doing 3 damage, you're doing 2; you're not countering the spell flat-out, you're allowing your opponent a chance to pay 3 to get it through.