This is not an analogous situation at all.
Maybe, but it is closer than your Everest comment.
Also, those examples you guys give of people who have toured successfully starting with little to no cycling experience are cherry picking the "winners". We haven't heard about the ones who tried the same thing and wound up way over their heads and abandoned the idea very quickly. I think it's unfair and misleading to imply that because a few carefully selected examples succeeded that everyone can too.
Well I can't avoid not mentioning those who bailed before I met them, but I met quite a few folks on the TA doing it as their first tour. Some were previously cyclists and some not. I personally had done a lot of biking, but it was my first tour as well. I have to think that given the number I met there are probably thousands who have done the TA as a first tour since it started in 1976.
I only met one first time tourist doing the TA who bailed and he bailed due to a knee injury. He was an avid cyclist before the trip but on his first tour.
I think that level of determination to finish is the primary predictor of success. Resourcefulness comes next. Some experience with packing for and living with their gear on some form of extended travel (backpacking, canoe camping, etc.) is quite helpful, but not absolutely necessary. Bicycling experience comes in at a distant fourth in my estimation.
BTW, even among those who tried a big first tour and failed to finish many probably had a positive experience. What is the big danger, that they might have to pack up and go home without reaching the other coast? That is not exactly the end of the world.