Look, it's unreasonable to expect any small forward to stonewall a center in the post. It's a completely understandable mismatch.
But one of the world's best defenders in LeBron James was utterly helpless when Nikola Jokic took him to the block. James didn't fall for any of the Serbian sensation's fakes, but Jokic still got the bucket, much to the delight of the home crowd.