Sure, it's not straightforward to roll tanks into Lviv. But I don't think not moving in a week whilst sustaining heavier losses than NATO sustained conquering and occupying famously difficult to conquer Afghanistan over two decades (a country which did collapse in a month after they left) was part of the original plan. Open for debate how much of the cities they originally intended to flatten but I can easily believe artillery bombardment was Plan B, with Plan A being the hope Ukraine's command structure would implode and they'd rapidly sue for peace
