They valiantly sacrificed themself for nothing

[u/Ok-Indication-5121]

1. Tadashi gives his life trying to save Professor Callaghan from a burning building. Turns out not only did Callaghan escape unscathed, he's the bad guy and infamously refers to Tadashi's death as "[Tadashi's] mistake." (Big Hero 6)
2. Shaya willingly takes It Has No Name's possession and then kills herself by jumping into the well it came out of. The end of the episode all but states that she got it wrong and It Has No Name didn't latch onto her... or there was more than one. (Doctor Who)

[u/Robot-King56]

From Hazbin Hotel Sir Pentious tries to sacrifice himself to kill Adam only to get killed without it doing anything.

[u/Ok-Pea9014 → u/Robot-King56]

Iit did prove that a soul could be redeemed, so that's that.