Guts is a character that struggles with severe trauma. He is a character who's literally been through hell and continues to fight it every single night. Despite losing everything he's ever loved, we see him struggle, contend and endure to survive, to grow and develop. Guts is the embodiment of what it means to be human; he can be heartless, he can be evil, he can be good, he can be generous, but he still has the capacity to love. One of his greatest qualities that sets him apart, is he has never, ever faltered from his will to live.
In Berserk, Skull Knight's words to Guts, "Struggle, contend, endure! That alone is the word of one who defies death," carry a profound message about perseverance and resilience in the face of adversity. This message underscores the importance of enduring hardships to pursue one's goals. His unwavering determination to continue fighting reflects the human spirit's capacity to endure and overcome even the darkest of times.