There are multiple ways to create difficulty in a game, but I think one of the simpler, more widely used methods is a very basic risk and reward system. To summarize the concept, a game will reward the player in some way (with items, exp, progress, etc…) if they take a calculated risk. That risk can be a death, loss of something, or anything largely detrimental in some way. Some games make this completely optional, and allow players to stay safe with other strategies, but many will force you in a roundabout way to takes that risk in order to proceed. This sort of thing is really common in dungeon based RPGs, and the main game I’m going to be using as an example is the Pokemon Mystery Dungeon series.
Pokemon Mystery Dungeon is a spin-off title of the main Pokemon games, only using some elements of it, but with a very different play-style and mechanics. The genre is classified as a Rougelike, defined by using procedural created dungeons to explore, turn based combat on a large grid, and a permanent death. The Mystery Dungeon subset of Rougelikes was first created by the Japanese company Spike Chunsoft, who produced and gave permission to create multiple series under that title.
Pokemon Mystery Dungeon, like other similar games, creates risk and reward scenarios by limiting save opportunities and resources. When a dungeon is entered, you are forced to take up a set number of characters, or in this case Pokemon, into the dungeon with you. These cannot be switched out for different ones until the dungeon is exited, which can only be done by reaching the end or having certain items. If your team is not balanced in strengths and weaknesses compared to the generated enemies, you will struggle the entire way through. And the main characters dying in Mystery Dungeon with no revival items means that you lose, and all of your money not stored away is lost, along with half of your valuable items.
Another limitation placed on the player is the small inventory. You can only pick up and hold a certain number of items while in a dungeon before you have to start choosing what you prioritize as most important. You can take items in with you, but if you find items within the dungeon that you like, you may be forced to use up or discard your supplies to keep what you stumbled on.This creates the need for developing a strategy and taking a risk by guessing what supplies you may need the most. You have to pack your bag efficiently and not just stuff it to the brim with healing items or weapons.
As a summary, Pokemon Mystery Dungeon’s difficulty comes from a combination of randomly created, and therefore unpredictable dungeons, a limited inventory for picking up new supplies, and forcing the player to create a balanced team with characters who have inherent flaws that must be worked around. Dungeons can’t be taken too slowly, or the player will get overwhelmed by enemies ganging up on them as they wander dungeons floors, or worse yet, run out of stamina and faint from weakness. You must move forward at a constant pace, but simply rushing ahead with no preparation will inevitably cost even more mistakes.
It might be a little hard to get used to for your first few dungeon treks, but you can’t get to the treasure without a journey first.