It deserves a blog post, but I'd say Lisp (at least Lisp in its mainstream Common Lisp incarnation) is easy to learn but extremely hard to master, since it allows many possibilities and paradigms, and because of the power of meta programming. So to master it, you would be familiarized with all the paradigms and you would know how to leverage meta programming, etc. Also, since it allows improving performance by going to low-level details (like observing the assembly output of your function), you would better know a bit of assembly/machine language if you want to be able to improve the performance of Lisp to approach (or equal) C code. So previous experience with low-level programming, at least with C, would be a good prerequisite.

But yes, using it for simple stuff is easy, and in fact, while I consider Python a great "first language to learn", sometimes I feel that Lisp isn't much difficult than Python, for the same tasks. Python is much easier to master, but then it is much more limited.