I always describe mining difficulty just as "I am thinking of a number between 1 and 10. If you can guess it, I will give you 50 points."

When they guess it after a few tries, I do it again but now "I am thinking of a number between 1 and 100."

After they try to guess it and get tired of guessing, then I say that "I am thinking of a number between 1 and 1,000,000,000,000,000,000,000" or something.

Then I explain that it is VERY EASY for me to change the difficulty of guessing a random number but it is VERY DIFFICULT for them to guess which number I am actually thinking about.

That has almost always helped normies understand how mining difficulty adjustments work.