Psychic is one of the more powerful psychic-type moves you can get in any of the Pokémon games. With a power of 90 and 100 accuracy, it is a hard move to top. This TM is hidden outside of Celestic Town, but you won’t be able to get it until pretty late in the game. Here is where you can find this TM in Pokémon Brilliant Diamond and Shining Pearl.
Before you can get this TM, you first need to obtain TM100 Rock Climb. This hidden move can be retrieved when you make your way up to Snowpoint City and Lake Acuity. Stick to the left when traveling through the blizzard section to find it more easily. To use Rock Climb, you need to defeat the gym leader in Snowpoint City.
Once all of that is done, make your way to Celestic Town. After you arrive, head out of town to the left. Next to the Route 211 sign, you will see a staircase. Follow the path up the staircase and fight the trainer next to the rocks you can use Rock Smash on if you haven’t done so already. After the fight, destroy the rock behind them and use Rock Climb on the cliff face. At the top, you will find the TM you’re searching for.