The way the Pathfinder Adventure Card Game works, your character’s deck is also their health. If you have to draw a card and your deck is empty, then you die. Its a bit like Magic The Gathering.
Typically, this happens at the end of your turn when you refresh your hand, and so the effect of this is to make characters with larger hand sizes weaker. They are more powerful in that they have more cards to do things with (items, spells, weapons, etc), but they are also more vulnerable.
Here is how it works: Each character has a deck of 15 cards. At the start of the game, they draw a hand based on their hand size. The fighter has a hand size of 4 cards, the cleric and rogue have 5 and the sorceress has 6.
As you do stuff in the game, you use up your cards by playing them. Typically, this means either discarding them to your discard pile, or ‘recharging’ them by putting them back on the bottom of your deck. You also lose cards by taking damage in a fight or from a trap. One hit of damage is one card discarded from your hand. If you run out of cards to discard from your hand, that’s ok because any extra are ignored.
It is quite good that you can never take more damage at a time than you have cards in your hand, but this is very, very deceptive. It is too easy to lose track and suddenly be at risk of death. If you empty your hand due to taking a bunch of damage, you will then have to draw your full hand size at the end of your turn, so you had better still have enough cards in your deck!
Suppose you are a fighter. You draw your starting hand of 4 cards. This leaves 11 in your deck. You are safe so long as you have at least 4 cards remaining, which means you can lose 7 cards by discarding either through use or damage before you are in danger.
Compare this to the sorceress. She starts with 6 cards in her hand. This leaves 9 in her deck. She needs to keep 6 cards in her deck to be safe, which means she can only discard 3 cards before she is at risk.
You can see how this system fits with the classic D&D flavour. Fighters are simple but tough. Wizards and sorceresses are powerful but weak.
I did also mention recharging, where you put a card back in your deck instead of discarding it. This is vital to maintaining your character’s survivability. Every recharge is one hit point saved. If you can get your character to a state where you are mainly recharging instead of discarding (either through choice of equipment or abilities) then you will find you can survive much longer. This is particularly relevant for spells, since spell casters tend to be weak.
Lastly, always, always, always watch your deck count. Short deck equals dead adventurer and we really don’t want that 🙂