Promises are threats; luck does not exist. The choice of that particular cipher was driven by two major factors:

It is not a mathematical puzzle, and while strongly sequential, the next logical value would be another directional arrow--the mechanically correct solution is both obvious and completely wrong.

And this puzzle is instantly recognizable to the sort of person who might have put it there.

However.

Where's the rest of it?

You're missing a button, there.