I don't think Jesus could have failed -- not in the least. Someone will say, "Well, so what did the temptations prove, then?"

I'll explain what they proved with an analogy. Let us recall the story of the Sphinx: Persons approaching this creature were required to answer a riddle posed by it in order to pass. Losers were summarily dispatched. The only way to get past it was to answer the riddle -- right?

Well, let's say that rather than answer the riddle, someone approached the Sphinx and, instead of playing its game, defeated the beast entirely by an overwhelming display of power.

So did he defeat the Sphinx? Of course he did. And he did so by rendering the Sphinx's challenge irrelevant.

As I see it, this is what the purpose of the Temptation of Jesus was -- it was to prove Satan to be irrelevant in context. Jesus experienced temptation firsthand (Hebrews 4:15) and knew what it was like, but this is not the same thing as saying that he could have fallen for it (and as Hebrews goes on to say, he didn't fall for it -- cf. Hebrews 2:17-18: "Wherefore in all things it behooved him to be made like unto his brethren, that he might be a merciful and faithful high priest in things pertaining to God, to make reconciliation for the sins of the people. For in that he himself hath suffered being tempted, he is able to succor them that are tempted.").

One could hear the Sphinx's riddle, and recognize its powerlessness before destroying the beast. In the same way, Jesus was tested, and was guaranteed a 100% victory. The Temptation was a glorious demonstration of what the Incarnation had accomplished.