Nothing contradicts that. SpaceX does do this contextually. Once they nailed down the Falcon 9 rocket, the boosters and the Merlin engine, they mostly stopped messing with it and focused on operational excellence. But to get to that point they failed fast, because it's the most effective way to get reliability.
See the last comment of my OP. The risk I'm poking at is a cultural one, where "failing fast" becomes an acceptable mode of operating, regardless of the context.
But it also shows "fail slow" later. My point is that "fail fast" is not some hard rule to abide by, but contextually dependent on the risk at stake.