The Crimson Binome
Hero
If you spend a spell slot to cast Fireball, and the enemy counters it, you're down one spell slot and you've wasted a turn. If you counter that counter, then you're down two spell slots, but at least you got your Fireball through. Given those two possibilities, there's no good outcome, but spending the extra spell slot is usually preferable.Although the counterspell can be cast at a higher level, doing so also burns up spell slots for other spells. How many spell casters want to burn up spell slot just to cast counter spells?
Suffice it to say, this is a fantastic deal for enemy spellcasters, who normally have trouble using up all of their spell slots in one day. They can pretty much counter everything you throw at them, forcing you to waste your own slots to counter-counter, and once you've done that they can get their own spell through without resistance since you've also burned your reaction for the round (assuming they survive whatever your original spell did to them). That also means you can't cast Shield this round, which is normally the wizard's best friend against fighter types.