This is the 5051st most frequent Turkish word.
gücünün
"Of his/her/its power" or "of his/her/its strength."
The word 'gücünün' refers to someone's strength and possession in the genitive case.
Bu işi tamamlamak için gücünün yettiğini biliyorum.
I know that your strength is enough to complete this task.
Here, 'gücünün' indicates possession (his strength) and emphasizes the noun 'önemini'.
En zor anlarında gücünün önemini fark etti.
He realized the importance of his strength in the hardest moments.
In this context, 'gücünün' is used to describe the subject's strength in a possessive and metaphorical manner.