Also when we (some) say "failed Messiah", they get the wrong impression of what the Messiah is and what he is supposed to do. They think its some miracle worker that waves his magic wand and all the problems go away. The lesson of Bar Kochba in NO, he is a regular person just a great leader (unifier) who brings military victory. Moshiah is just "the anointed one", and not some demi-"g(0)d" many people imagine.
Today we hear he is supposed to be a great "kabbalist", "Talmid Hacham", and other such things. BUT with Bar Kochba (who failed in the end) but was supported by Rabbi Akiva we see he is a military/political leader. Also another example is the vision of Yaakov (ISRAEL) to his sons where he sees Shimshon and during his vision he thinks he is the Messiah, until he sees him fall (die) as well and then realizes that he is not.