And by "failed" I mean it seems clear from Matthew 24:34 that first generation Christians believed the end times would occur within their lifetimes (assuming that account is credible,) and such a belief is consistent with every other apocalyptic cult, Christian or otherwise. Like Seventh Day Adventists, Christians do keep kicking the can down the road, but just as the book of Revelations more likely refers to Nero Caesar and a belief at the time that he would return from the dead ("Nero Redivius[0]") than some future nuclear war where the "locusts" are really Apache helicopters[1], so Christian beliefs about the second coming should be assumed to apply their own cultural and temporal context, rather than some as yet unknown future millennia removed.
Obviously the cult as a whole has been very, very successful.
[0]https://en.wikipedia.org/wiki/Nero_Redivivus
[1]I know people who believe this, and they'll claim it as evidence of the Bible's divine prophetic power.