I agree with those who have said Patience. You could be the greatest player ever but without patience it would all be wasted. It takes years to develop the kind of patience needed at the top level IMO.
I think that mathematical and psychological abilities are important, it is important not only to count cards, but also to be able to read your opponent, and it is important to work not only on the game, but also on yourself
The most essential quality of a poker player is a combination of strategic thinking and the ability to read opponents, known as "poker face" or emotional control.
T The best quality is to be calm and resilient. For example, I have difficulty dealing with anger when I lose to low hands, especially when I lose to a river card.