# Building Better Decks: Card Advantage
So we've just touched upon making efficient use of your mana to win games. Honestly, I think mana efficiency is the deciding factor in 70 to 80% of all games; build your decks and play with that in mind, and you will easily rack up wins. But what about those remaining games? They are mainly decided by how you manage the other main resource of Runeterra: your cards.
# Card advantage: More (virtual) paper is better
Another concept borrowed from Magic, card advantage refers to the idea that when the game goes long, the player who has access to more cards is going to win. "Access" here basically means "in your hand or on the board". At the most basic level, you can just add up the number of cards in your hand + units on your board, and compare it with your opponent's total. Whoever has the higher total is said to have card advantage.
Why does that work? Well, I typically expect one of my cards to trade for one of your cards. My Precious Pet for your Brightsteel Protector; my Thermogenic Beam for your Thresh. Eventually one of us is going to run out of cards, giving the other player the advantage. The last unit standing should be able to go the distance.
But wait, you might say... both players start the game with 4 cards each, and both draw 1 card per turn! How does one player gain an advantage over the other?