The horse episode rests on hearsay from Davide Fino, the lodging-house keeper, told after the fact; no contemporary document confirms it. What is documented: Nietzsche's breakdown in early January 1889, the mad letters signed 'Dionysus' and 'The Crucified,' and his removal to Basel and then Jena. The horse may be literature that happened to nobody.
Beloved by storytellers: the man who preached hardness breaking on the rock of a horse's suffering, pity as the true last word. Tarr's 2011 film The Turin Horse turned the anecdote into apocalypse. It is too good to check, so mostly it is not checked.
Read from inside the philosophy: the collapse as identification with all suffering, the crucified and the god in one signature, the self finally unable to maintain the hardness it prescribed. The hammer meets the anvil and discovers they are the same flesh.
Did he finally see the world as it was, or was that the moment he stopped seeing it at all?