I got into reefing back in the summer of 2006. It was a real struggle for me despite the fact I did my very best to do everything right; I read, asked questions, prepared, ect., but everything went totally wrong. I started out with a brand new 29g. I cycled the tank for over a month doing the dead shrimp thing. I also bought 30 lbs. of live rock from LA and cured it downstairs - a 20 day project. About two days after adding the newly-cured LR into the tank (it had a pair of clowns and a cleaner shrimp in it) the bottom broke out at 3am! I was able to save my fish but at that point, I thought I was done. I mean, after preparing for a month doing it right, my tank was KIA after just a few days.
Well, the guy running the LFS took pitty on me and gave me a used 40g breeder. That's where everything went really, really wrong and I couldn't figure out why. Basically, my fish kept dying -- fish that I *really* wanted to keep alive and healthy. I maintained perfect RO water, salinity, Ph, temp, tested every day, etc. Still my fish kept dying. After about 6 months I found myself totally burnt out and finally took what fish I still had back to the LFS and give him that tank back.
Now that some time has passed, I really started thinking about what went wrong and I believe I now understand what happened. I have reason to believe that tank was a hospital tank for a customer who had a much bigger system. God only knows what that 40g might have been laced with, was it coppered? And I'm pretty sure that was the problem. Back then I simply didn't have the knowledge or experience to figure it out.
So in a nutshell, something as simple as that crushed my interest in keeping a reef tank. As a side note however, I do not consider myself "out of the hobby" -- more like in hiatus. I do miss it and as soon as possible I'll be purchasing a *brand new* 75g and starting all over, but that is several months away at best.
Given my story, I do expect that some other beginners probably have equally hard times and simply don't have the knowledge to figure it out so they end up leaving for some other hobby -- unless they're like me becoming truly attached to the hobby and unable to stay away from it for very long - despite it all.
-Ryan