What happened during the Kharkov offensive is why they are nervous, but things have changed so much since then. Also during the Kherson offensive the Ukrainians lost a lot of soldiers, way more than the Russians. Although it was a good victory, and Kherson was good strategic city because it was a strong foothold over the Dnipro river, it came at too great a cost, and Russia could of held it if they wanted too IMO. I personally think the Russians should not of retreated, but they did preserve their forces. The Russians decided around September to make this a long war of attrition and to take no risks, because time is 100% on their side. I can't criticize that strategy, because it involves almost no risk. If the Ukrainians are successful and score a total victory by taking Crimea, then the Russians really were a second grade military. To me Syria was already a good testing ground of NATO equipment and strategy against Russian equipment and strategy, and Russia won that battle IMO. So I can't realistically see a Ukrainian victory.