Honestly, the only misconception I had when I started was that "running is boring." And, that was only in my head because some stupid human being had said that when I said I was going to go for a run (summer training for my HS frosh year of XC.)
And it was boring, for about 5 minutes, when I thought "geez, this IS boring," lol, and then my next thought was "Well, I'm going to have to find a way to make it not boring, how could I do that?"
And the next thought, or the answer that came into my mind was...was the answer...and running was never boring again.
If you don't know the "answer," then maybe you aren't meant to be a runner.
I would say, that the greatest misconception that is perpetrated out there, is "work hard and you can make it," and other rote positive thinking, well meaning, actually shallow pieces of advice.
Rote optimism is better than rote pessimism, today, however, with all the sports science we have etc., I actually respect runners who had their VO2max and everything else tested...and decide to run for fun and fitness and not for dreams.
As I've said before, pursuing glory or success in running is about the stupidest thing you could do -- the odds of success are about the lowest of any endeavor you could think of. Your potential is 100% determined by your genetic luck.
On the other hand, I got good enough to compete in Europe for one season, if I hadn't "dreamed the dream," who knows if I would have ever gotten to Europe -- a trip that widened my worldview and led to many more trips.
So I don't regret it; I do in retrospect wish there had been more realism around me in my early days and era (which I think there is today, due to such a greater access knowledge etc.) HS coaches, teammates, friends, all well meaning etc., putting the Olympic dream in you at say age 14...is very unrealistic.
Another way to put it is, I think there are a lot of, say, high school 2:00min 800 meter runners who work as hard as the few sub 1:50 high school 800 meter runners.
Another aspect, something others have mentioned before, is that when they started out running they wanted to be good at X and discovered their best ability was at Y.
I've seen guys and girls start out wanting to be good at the 400 and ending up in the 1600 (or the 3200 in case of one girl.). I knew a guy who wanted to be a 5,000 runner only to find himself breaking 50. in his 4th 400 race.
Run for the love of running, is the best plan.
Fate/Genetics/Luck will take care of the rest. Yes, hard work and proper training are important. I think more people work hard than this board tends to give credit. Yes there are always examples of people who weren't really working hard, then do, and have breakthroughs, but I think most kids, the majority, do the work put before them and do their best. ("Proper training," does include both working hard and the guidance to not over work, and to recover etc.)
This was actually a very good question, and one of the most under discussed topics about running: Misconceptions.
Since so few people can make it to the elite level, let alone make a national or Olympic team -- the best goal to have is to protect both your outlook on running, and your running health, so you can have running as a life long fitness or health endeavor.
Good Luck!