Ukraine can win, they just can't meet the bulk of Russia's forces head on. They can, however, defeat Russia in time, and with the support of allies that time can be short. If Ukraine comes out of this an EU member then they will have profound and victory that will benefit Ukraine for generations.
This is an opportunity. Putin has rolled the dice and thrown the first punch. Russia needs punishment in the form of military humiliation and Putin has given the West a once in a century moment to deliver exactly that.