The player should not have to figure "what to do"
just "how to do it".

Logical contradiction where 2 things are seemingly
in conflict with one another.

Think outside the box, about how the game works
This discovery becomes part of your toolbox going on

Lure the player that he knows how to beat the puzzle.
Why?

1. Gives the player a starting point
2. Help to build a mental model of the puzzle
3. Ensure the player fails the puzzle the 1st time
4. Focus the player on the puzzle Catch

Pretty minimalist, with few moving parts,
giving the feeling that it shouldn't be hard to beat
Also: provide clear feedback

No puzzle is given to the player in isolation
Criteria to judge a puzzle difficulty:

1. Number of possible solutions
2. Number of steps required
3. Number of options a player can choose at each moment
4. Number of mechanics the player needs to be familiar with