A pretty common answer.
But, it still means the plans of God were thwarted, which Scripture says can't happen.
Only if I limit myself to your own personal (and tortured) interpretation of scripture.
I choose (scary word!) not to be so limited.
Didn't God create man to love Him? How could we love Him without free will? And if we have free will, doesn't that also enable us to reject Him? And if we choose to reject Him, even despite His gift of salvation, whose fault is it? Why would this be God's failure? Salvation works for those who choose it. It's not God's fault that they haven't chosen to accept His gift.