[foobarbaz33]

Two things mostly unique to lisp.

    1. Live editing, where your code evals and applies to the running image as you write it in your editor. 

    2. Easy full-proof macros.  Not to be confused with the text-wrangling style of macros you would find in C.

Most languages cannot provide these things. And they're really really nice things to have.

Why aren't features #1 and #2 more popular in other languages? People don't miss what they never experienced. And both of those features require design at the runtime level and syntax level of the language to be implemented in a way that doesn't suck. They can't just be bolted on to a any random language like C++. Even though C++ likes to bolt on every feature it can.

Why would you learn lisp? To get features #1 and #2 in hopes of increasing your productivity.

[Qem]

Smalltalk is strong in this front too, at least regarding (1). Perhaps not (2), but its flavor of metaprogramming stands by itself. See https://medium.com/smalltalk-talk/lisp-smalltalk-and-the-pow...