The definition of insanity is repeating the same mistakes over and over again and expecting different resultsHowever, the quote had been mis-attributed to a variety of people including Albert Einstein, Mark Twain, Ben Franklin, and others. However, its real origin is from a Narcotics Anonymous newsletter dated 1981 (scroll to page 11). Which means this is a quote about addiction.
Which makes it oddly appropriate about MLMers, specifically, about SERIAL MLMers, those people who keep joining one MLM after another, looking for "success" and kept spending money on the products, on his or her upline's advice, always having an excuse (the leader made a mistake, the market wasn't ready for us...) As they keep doing the same thing over and over, hoping for a different result.
One such example was the "confessimonial" on SaltyDroid... a story by "Roger Wilco". RW described a relationship with a woman who was heavily into MLM, spent well over 200K into various MLMs over 7 or so years, and in the end, chose MLM instead of him, never finding any success.
Addicted people, by certain "colloquial" definition, are "insane" because they are driven by their addiction into making choices that no "ordinary" people would make.
And MLMers, similarly, are "addicted" to MLM that they make choices that no "ordinary" people would make. That is a form of insanity.
Previously, MLM Skeptic have discussed the social cost of MLM, and concluded that participation in MLM comes with a heavy social cost that many people are unaware when going in (they thought it's just a business) and simply cannot afford in the long run. Some unscrupulous MLM leaders use cult tactics to force members to conform as well as feed their addiction for social approval by their peers (which driving them apart from their friends and family). This cult indoctrination makes MLM extremely dangerous if you met with the wrong upline (and there's no telling who's a good upline and who's not merely from a few meetings).
Furthermore, in the RW confessimonial referenced above, the partner seems to be no longer making decisions that an average person would make. By the very colloquial definition, the partner is "insane". She made choices that no "normal" (sane?) person would make: kept dumping money into MLM ever after losses year after year, and in the end, chose MLM instead of love.
One would expect that repeating what was done before and hoping for a different result is merely gambling, and wishful thinking, yet that's exactly what the cult encouraged as a part of their indoctrination and addiction. Your family and friends don't understand. Leave them. We are your new family. You will succeed with us. We promise.
Then once you're in, and you realize you're failing, you're fed with excuses (it's not our fault) and victim blaming (it must be YOUR fault!) Add a bit of confession (I did not sell to enough people, I failed the group) and you have a cult. You don't even need a confession... You just need to do the opposite: recognize all the people who did meet the goal, and it's clearly implied that everybody else failed.
And that does NOT lead to a happy ending. In worst case scenario, it leads to depression and suicide.