 What makes Lisp hard to learn?
hga: Hmmm, I started learning it in 1979 (sic) when my major experience was FORTRAN, BASIC, and an obscure language called PPL who's major features I hadn't taken advantage of (it was for a summer class).  I'd toyed with/looked at COBOL, PL/1 and C.The biggest thing, I think, is that it's based on expressions rather than statements, which is rather a different model than the Algol family (more or less) languages mentioned above.  And for me, learning the importance of indentation for code comprehension, but that had already started with my learning C.And then there's recursion; you can't do idiomatic LISP without it (The Little Lisper or nowadays Schemer is good for that).Ideally you'll also learn functional programming; optional in Common Lisp, hard to avoid in Scheme, and there's little point in using Clojure without it.Frankly, I find it delightfully simple.  The conceptual base is small, the syntax of parens, atoms, immediates (e.g. numbers) and special forms (e.g. if) makes is a very regular language, no "cancer of the semi-colon.It's really quite nifty, and of course back then there was pretty much nothing faster with which to develop software.  You mostly just have to unlearn some stuff and be willing to put in some effort, which will be well rewarded.