There are four basic, or visible, stats within the game; Health, hunger, thirst, and fatigue. These stats are crucial gameplay elements, each one going from the values of 0-100. These stats tend to have effects on one another, and if they go to low or too high then you run the risk of dying. All basic stats can be changed in-game for better or worse, indirectly or directly by the player. Certain states will effect the player's stats, and base stats can be changed through the game code.
Health is, as you might expect, the "life" of the player. Health can be reduced through a variety of ways, and regained as well. The health stat will usually start at a full 100, which is the highest you can achieve. When certain events such as sleeping without a shelter, eating dangerous foods, or getting attacked by hostile units occur, your health may decrease. When your health decreases to a value of 0, your player will die and you will have to pick up from the desired save slot. Your health will also go down if your other stats achieve 100 or if certain states are applied.
You can regain health by eating most safe foods, by sleeping in a shelter, or by using a medikit. The invincibility state will make it so that it's impossible for you to lose health, and health is a stat that applies to all dropped items, objects, and units. The regeneration state will cause you to regenerate health slowly over time.
It is represented by the rainbow bar at the top of the GUI.
Hunger is a stat that is centered around edible items or lack thereof. Safe foods will decrease this stat, and this stat will increase on it's own over time. Events such as sleeping or swimming will cause this stat to increase, and when this stat reaches a capped value of 100, you'll begin to lose health until the hunger stat is lowered. This stat will also slightly increase when doing certain menial actions, such as fishing, using a tool, or foraging.
It is represented by the green bar near the top of the GUI.
Thist is a stat that is very similar to hunger, except it is drained and increased in different ways. It can be increased even by certain safe foods that are dry, by drinking salt water, or by the same natural methods that hunger increases. When it reaches a value of 100, your health will begin to drain until you can lower the value.
It is represented by the blue bar near the top of the GUI.
Fatigue is the amount of "sleepiness" your player experiences, which will increase throughout the day or when you perform specific actions, and also when you eat toxic mushrooms or hemp leaves, or if you use a joint. Like other stats, when this reaches too high of a value you'll begin to lose health until it can be lowered. The main way to decrease the fatigue stat is by sleeping, which will completely reset it and cause time to pass. Cetain foods can also lower it, including bananas, coffee fruits, and bitterroot.
It is represented by the purple bar near the top of the GUI.
There are other stats within the game that are not directly revealed to the player through the GUI or are only available through certain events.
Air is a stat that will only be visible through a bar when the player is submerged in water, in which case it will slowly decrease until it is empty, and you will begin to drown, or until you emerge from the water and the bar disappears. This stat can go beyond what the visible bar shows if the player consumes an air potion, in which case the player will be able to "breathe" underwater for some time.
It is represented by a blue bar in the center of the GUI.
Speed, simply enough, is the rate at which the player or unit can move. The average player speed is 1.6, and this can only be raised in-game through the potion of haste, which induces the bloodrush state.
It is not represented in the GUI.
The eyes stat is the field of view that the unit holds, describing how much of the surrounding area the until can visually detect at any given moment. It cannot be changed in-game. In non-player units, it is the only deciding factor other than AI that decides whether or not they can detect the player at all.
It is not represented in the GUI.
The max weight stat describes how much weight a unit or object can contain. The base max weight stat for the player is 25000, and can technically become higher if in possetion of butterflies due to their negative weight value. If something is too heavy to allow you to carry, you will simply not be able to pick it up.
It is represented in the rucksack menu.