Who said that Our Lord would have encountered "no difficulties" or wouldn't have been "fully human"? What we're saying is that He would not trip and fall out of mere clumsiness as depicted in the film, resulting from lack of control over His Body and / or being inattentive to where He was walking. He spent His entire life in penance and subjected Himself to all manner of suffering, but of His own will.
To attribute to Our Lord various frailties, however, that are the result of fallen nature is not to "fully humanize" Him by any stretch. That's one step away from saying that He would not have been fully human had he not felt the tug of His lower nature working against His will during temptations, that if, say, He were to have seen a beautiful woman, that His lower nature was drawing Him to impurity as happens to fallen men. We have to distinguish what is fully human in an unfallen human being (i.e. what is essentially human) and those things that are the product of Original Sin. Since He did not labor under Original Sin, Our Lord's Body was under complete and absolute control of His will, an extension of his intellect and will, and was limited only with its innate capabilities. So for instance, at some point His muscles gave way under the weight of the cross and could endure no more. His heart gave out from His suffering on the Cross. But that's differen than saying He could fall out of clumsiness and inattentiveness. I agree completely with Gladius. I had never give this much thought, but once he said it, it makes perfect sense.