Why couldn't Adam and Eve keep both commandments?

I hope this question is unique here, but I assure you I have searched and have not yet seen it. (This question is close, but not quite the same.) Adam and Eve were given two commandments: 1) Multiply and replenish the earth, and 2) not eat of the forbidden fruit. From what I understand, some Christian denominations believe the commandments to be paradoxical; one cannot be kept without breaking the other. Within the scope of those Christian denominations which view the two commandments as both impossible to keep while in the Garden of Eden: Why couldn't they keep both of these commandments, for surely they would have if they could?