Lisp will free your mind.

Allow me explain this blithe sound-bite further. Almost every non-lisper is wedded to some fairly constrained form of thinking, largely driven by their programming language of choice. So, for example, most Java programmers will begin thinking about any new problem in terms of objects, classes, interfaces, beans, jars and the like. Haskell programmers immediately start thinking of types and type-classes and other higher forms of abstraction that they can use to simplify the programming task, and C programmers immediately start thinking about structs and functions and memory allocation/deallocation strategies.

Here's the thing about Lisp (and more specifically, my favorite variant of it: Scheme). It constrains you with almost nothing. You can program with it in any paradigm you choose, at any level of granularity. This broadens your design space tremendously. This is both liberating and scary (freedom always is). Your program design problem now becomes more about seeking the best fit of your solution from a very large collection of paradigms available to you, and if you are so inclined, invent a paradigm that works best for the problem at hand.

Apart from the functionality of your program, 'Best fit' here could mean any number of things: Productivity, Performance, Size of code, elegance of code, ease of teaching ... or what ever combination of things you are trying to optimize. (my own optimizations often are a combination of performance, minimalism of the code, and elegance of the abstractions).

This is a *very* different way of thinking, and most programmers will not spend enough time with Lisp to ever get it (also the reason why Lisp has few but ardent adherents). But once you do reach this level of understanding, nothing else will suffice.

PS. Thanks for the A2A ... fascinating question.