Though prior experience proves nothing about how this episode will end, staying in the fight long enough to wear out your enemies’ resolve has led to success without winning every battle. Consider:
American Revolutionaries
North Vietnam and the Viet Cong
Taliban
Russia is in a good position to gradually choke supply lines and wear down Ukraine, but the power behind the throne might tire of massive financial losses. Time will tell who holds out longest.
Think also about Napoleon against Russia. The Russians denied Napoleon the set piece battle he wanted, hitting his weak points and attacking his supply lines. If Ukraine can hold on they will bleed the Russians white.