From dieyoung

When a New Game is started, Die Young lets the player choose between two Modes: Adventure and Survival.

Adventure Mode is described as "The best way to enjoy the experience and the story. Recommended for new players."

Survival Mode as a "Higher difficulty level for a grueling experience. All blood, sweat and tears."

Apart from the most obvious difficulty differences (which can all be modified at a later time, see below), the two Modes differ in how they let the player craft a Campfire, which is useful to manually save anytime during the game: in Adventure Mode, you start the game with the Campfire recipe already unlocked in your Craft Menu; in Survival Mode, you need to find the recipe to unlock it (also, a Campfire in Adventure Mode requires fewer materials to be crafted). This is the ONLY feature that CANNOT be changed after the game's started, so keep that in mind if you're considering to play in Survival Mode.

One more difference is the starting storage capacity for Materials (Adventure Mode let you take with you 2 more units for each type).

As stated before, regardless of the Mode selected by the player at the beginning of a new game, difficulty can be customized anytime through the Difficulty Settings (from the Options Menu). There are three Presets (Survival, Adventure and Leisure) and five different gameplay factors that can be changed independently from Low to High (the Preset is then classified as "Custom"): Damage Resistance, Stamina, Attack Strength, Hydration Level, Weapons Durability. The following is a table that shows how these values affect gameplay (Survival preset sets all values to Low; Adventure preset sets all values to Medium; Leisure preset sets all values to High):

Settings Effects Low Med. High
Damage Resistance All damage received is reduced by: 0% 20% 50%
Stamina Stamina consumption is reduced by: 0% 20% 50%
Stamina recovery is speeded up by: 0% 20% 50%
Attack Strength Damage dealt by Daphne is increased by: 0% 50% 100%
Hydration Level Hydration consumption is reduced by: 0% 20% 50%
Hydration depleting delay after last drink / food: 100 s 300 s 500 s
Weapons Durability Durability is increased by: 0% 200% 500%

In addition to these settings, you can also enable or disable two other features: Perception and the Climb Aim Assist.

The Climb Aim Assist reduces the sensibility of mouse or gamepad when the cursor is close to a handhold in climbing. This prevents any failed jump it may occur if the cursor is unwillingly moved right before pressing the jumping button.