The quote "Is a knife evil? Only if the wielder is evil" from Rick Riordan's book, The House of Hades, suggests that tools and weapons themselves are not inherently good or bad; rather, it is the intention and character of the person using them that determines their moral value. This highlights the importance of individual choice and ethics in shaping actions and outcomes.

In essence, the quote encourages readers to reflect on the nature of good and evil, emphasizing that responsibility lies with the user. It implies that judgment should focus on the wielder's motives and actions rather than condemning the object itself. This perspective invites a deeper understanding of morality and the complexities of human behavior.