Because I thought that passing a save achieves the same thing as iron heart surge, without the preventing sunburn, gravity, crime, not having a sandwich and not being Asmodeus that Iron Heart Surge as written comes with.
Saph's big list of effects it works on is too clunky, Sophismata's is too long and every other fix allows you to break out of one effect, but not ones that it would be most useful for. This just allows you to say "no" to your DM and then **** his favourite new NPC for being cocky once per encounter, which is what IHS should have been in the first place.