The more you play poker, the more you understand that the cards are just one piece of the puzzle, in my opinion. Anyone can draw kings or aces during a session, but that doesn't mean they'll get the same results every time. The key factor is how you carry yourself in situations where you don't have a premium hand, when variance isn't working in your favor or when you feel the need to be overly aggressive.
The cornerstone of the game is patience and self control. Discipline enables you to maintain your plan even when your emotions are pulling you in the other direction, while patience prevents you from acting impulsively when the moment is not appropriate. These two characteristics alone can prevent you from making a lot of errors.
On top of that, the mental side is about resilience. Can you stay focused after losing a big pot ? Can you avoid tilting when someone sucks out on you ?
So yes, i would say poker is much more about the mind than the cards. The cards create opportunities, but your mindset decides your results.