The difference is that Russia might be successful pretty quickly...

The difference is that Russia might be successful pretty quickly ( past incursions considered)... Therefore fighting back is a reasonable option.
Ukraine are going backwards in areas they have held and fortified for about 10 years. In this situation fighting back doesn't seem to be such a great idea.

But hey, if Ukraine still hold the Kursk areas in a month, maybe Russia should have negotiated.

ps: I didn't suggest you should go to the front. You can just be on a Kyiv train and say the wrong thing.