What does “je mehr … desto mehr” mean in German?

A minimalist shows her flat and explains why she keeps less. She says “je mehr Platz ich habe, desto mehr möchte und muss ich auch besitzen” — the more space I have, the more I want and have to own. It has two parts: “je mehr” opens the condition, “desto mehr” gives the result. Notice the word order: after “desto”, the verb follows right away. Here it explains why she finds three rooms are too much.

She says: “je mehr Platz ich habe, desto mehr möchte und muss ich auch besitzen” — “the more space I have, the more I want and have to own.” The pattern is “je mehr X, desto mehr Y”: as one part grows, the other grows too. You can swap in other words: “je mehr ich übe, desto besser werde ich” (the more I practise, the better I get); “je länger ich warte, desto teurer wird es” (the longer I wait, the more expensive it gets); “je weniger ich besitze, desto freier fühle ich mich” (the less I own, the freer I feel). After “je” the verb goes to the end of its part; after “desto” the verb comes right after the comparison word.