I learned PHP years ago, never got past the "futzing around making a basic CMS" stage with RoR (I currently do most of my work in C# and ObjC). I'm sure I'll be politely corrected in this view, but the piles of add-on gems and scripting utilities that characterize Rails-in-practice meant that Rails struck me as kind of a moving target.

Coming from PHP where basically nothing happens unless you make it happen (for better and very often for worse), I found Rails confusing once you got beyond easy Active Record calls and into using gems. There are tons of add-ons that do useful things, but they do a lot of their work behind the scenes assuming adherence to certain conventions—which, I know, is a strength as well as a weakness, I get it. But that increases the difficulty of jumping past the stage of following a tutorial and just installing one persons collection of gems, scripts and other helpers.