Difficult? You betcha. That's why most elevator pitches run to a page and are full of useless buzzwords and explain nothing. It's much easier
But if you want to ever be effective, you need to be able to tell your prospect what your product or service does, simply, and in a sentence.
The best way to do that is to write something long. Then ruthlessly cut unnecessary adjectives, buzzwords, sentences until you are left with your 1 sentence.
And for those who don't want to click a link, here is Messi's Mad Libs approach to making a good elevator pitch:
"(My company) has a (defined offering) to help (a target audience) (solve a problem) (with our secret sauce)"