Three years into a conflict that was supposed to end in days, Ukraine has emerged as the most battle-hardened force in the West. While NATO debates doctrine, Ukrainian forces have rewritten the rules of peer-warfare through blood and rapid iteration-from FPV drone swarms to decentralized command. This hard-won knowledge has a short half-life; the window for NATO to integrate these lessons is closing. The Alliance must decide if it is humble enough to let Ukraine co-author the future of Western defense.