I once thought I gave my players the simplest puzzle ever. A journal said, “I found it all in a book, 5x7 Shakkan.” Figuring they should look for the book, they proceeded to the city’s library and found the author Shakkan’s section. I then informed them the books were shelved ten to a row, ten columns high. If this were a video game, you’d select the bookshelf and suddenly be scrolling across a book grid. It would become pretty obvious that you need to select the book on the 5th shelf, 7th over. But in a world where player’s can do anything, this connection was not made. Instead of making things interesting, my puzzle brought the game to a halt for 15 minutes. Eventually, I had to solve the puzzle for them.
Puzzles work great in video games. Your experiences teach you to only interact with objects that glow blue, and you understand your limitations. Your inventory system is finite, and many of your items are only usable in certain situations. In a tabletop RPG, if you're designing a puzzle with a single answer, you’re forcing your players to either understand it immediately or ask for help. There is no room for the players to experiment or be rewarded for ingenuity. Therefore, any likely solution should be a likely answer.
Making up your own puzzles is not easy. Before your game, you probably took to the internet to find something for your next adventure. Taking it as is or changing it to fit your adventure still hasn’t fixed the problem. You didn't come up with it, so it’s hard to adapt it on the fly. Altogether, you’ll be so concerned with making sure it’s communicated correctly that you no longer have fun in its execution. Instead, make up your own general puzzle and let the players decide how to solve it.
In a room, there is a door and a pool of water. At the bottom of the pool, there is a button. When this button is pressed down, the door opens. When the pressure is released, the door closes. The button requires 10 lbs. of force to activate.
Perhaps they go get rocks from a previous area, or maybe the mage holds it down with their mage hand. They will probably surprise you, and as DM, you will suddenly have more fun.
To add complexity, add more elements, picking things you know your players can do but are simple enough to have multiple solutions.
In a room there is a door and a pool of water. At the bottom of the pool, there is a bar connected to a chain, pulled tight, running through a hole in the bottom. While the bar is lifted, a 3 three inch hole appears on the wall, leading to a small room with a button that opens the door.
You know the barbarian has enough strength to pull the bar and enough constitution to hold his breath. The group’s druid can turn into a snake to fit through the hole and press the button. But maybe the druid summons an octopus to work the bar, and the group’s rogue shoots the button while the barbarian holds open the door. This gives you an adaptable solution that lets you reward the players for their ingenuity.