せいで vs おかげで — can せいで ever be positive?

Question

Learned せいで as always negative blame (雨のせいで遅れた) and おかげで as always positive thanks (先生のおかげで合格した). Saw a native use せいで sarcastically for something good and got confused. Is that just sarcasm or a real usage?

Accepted Answer

せいで is grammatically fixed to negative/undesirable outcomes — that's baked into the pattern, not just convention. What you heard was almost certainly irony (お前のせいで優勝できた笑 kind of joke), which works precisely because the listener knows せいで 'should' be bad. おかげで has a similar flexible sarcasm in reverse, but the neutral default of each stays fixed.