To follow up on what he posted, “-100%” is not the same as multiplying by zero. If a node or ability adds to their potency, you’re back above 0 and taking damage.
If torch has 0 smoulders, one incinerate will deal 112% damage, two incinerates would deal 124% damage etc. Surfer reduces this by 100%, so if you have one incinerate you'll be taking 12% of the total 112%, and with two incinerates you'll be taking 24% instead of 124%. As torch quickly builds smoulders, his incinerates are gonna keep doing more and more damage, multiplying the damage by 400, 500, 600% etc. Since surfer only takes 100% away, he's still gonna get melted pretty quickly