The Onion released a list of actors who remain popular despite a long string of bad projects. Since film is not exactly an actor's medium, it makes sense that the on-screen talent could have a wildly varied CV. Less so for directors: their output tends to be more consistent in tone, character, and quality*.
Nonetheless, I have my own "unbreakable" auteurs: directors who I stick with no matter how unspeakably painful their latest efforts have become. Hal Hartley has always been an acquired taste at best, but hasn't really spoken with a clear voice since Henry Fool. Tom Tykwer amazed with Lola and Krieger, but has fallen decidedly flat with everything since. The less said about David Lynch the better. Yet, I can't stop myself from seeing their latest works regardless of how much I have been disappointed**.
What's the common theme? Unbreakable directors favor ambition over execution. Ideas over thrills. They don't set out to make crowd pleasers, so failure isn't ameliorated with the sugar of stupid fun. And when they stumble upon success, it is so powerful to experience that it's worth the infliction of a dozen Lost Highways. Pity that such success happens so infrequently.
* Even famously diverse Ang Lee has a string of thoughtful humanism in everything from The Wedding Banquet to the Hulk.
** Seriously: Perfume? Now Tom's just a dirty old man. Really, really dirty. UPDATE: Nathan Rabin just reviewed Perfume and concluded that it's a "secret success". I can see where he is coming from, but that doesn't change the fact that the last half hour kills the film.