Not so. Any challenge with random elements can become impossible. The patterns that appear are not guaranteed to be passable.
That's a good point, but I kept that in mind as well when creating the challenges
The random variables provide surprise, and the constant variables keep the structure so it doesn't become impassable
The constant enemy units have a pattern to them designed to be passable when timed correctly, in fact most of them have numerous openings in their pattern -- the one or two random variables cannot be regulated really, but the player has to time the random variables with the constant variable correctly to navigate the challenge
It's always passable no matter how many times you come against it or re-do it, you just have to both wait for the right moment as well as execute it correctly
In short, it's navigating the same puzzle you already know how to solve, but with a few extra pieces to distract you while you do it each time, random pieces with random shapes, if you know what I mean