I don't mean to get into Ukraine Frontline analysis too much. But the shortage of ammo/supplies, a lack of preparations for key cities like Avdiivka, and an increase in Russian manpower has resulted in a number of slowly cascading events.

More specifically, Avdiivka was the key to many things. As the Russians had done before with the fall of Bakhmut, which was complicated by the fall of Soledar north of it, which itself was complicated by the fall of Yakovlivka (north of Soledar).

A lot of people really discount the Russian mobilization as one of the big turning points of the war and I'm not sure why