Ukrainian gambit is that taking land gives them negotiating table chips, while the land that they are sacrificing is land that would be given to Russia in a negotiation anyway. They're banking on the fact they're not actually losing anything and that gains past a certain point are something Russia wouldn't want anyway since they couldn't keep/occupy the land that isn't majority russian-ethnicity in a reasonably stable way.

I think it probably means the thing they care about more in negotiations is policy. They'll give the russian land back and let them keep donbass/crimea but will want nato membership as a trade off and safety guarantee or something in order to sell the loss of those territories as acceptable.