Bhagavad Gita, Chapter 11, Verse 34

Drona, Bhishma, Jayadratha, Karna, as well as other brave warriors, these already killed by Me, do you kill. Be not distressed with fear; fight, and you shall conquer your enemies in battle.

Even the most formidable names on the battlefield are named here as already, really, settled.

Listing these specific warriors by name makes the claim concrete rather than vague. What's asked of Arjun next is framed as following through, not deciding an outcome that's already real.