First, no one was expected to keep it because no man is perfect. But everyone is expected to try to keep it. It is okay to honestly try even if you honestly fail. That's what Judaism teaches, so I don't know where Paul got his ideas. Maybe he just made them up to sell his story (after all he admits he was all things to all men as long as they believed him!).
Second, no observant Jew would ever say that the Torah can be fulfilled. The Jews believe that the Torah was written by God before the foundation of the world (and merely dictated to Moses). Furthermore, because it is the very own God's word, it is eternal and is to be observed forever. In other words, it cannot be fulfilled.
So, the Jews raise their eyebrows when they hear that Jesus (an observant Jew who believed the Torah) said he came to fulfill the Law! This is equivalent to a Mormon like Glenn Beck telling Christians that Jesus and Satan are actual blood brothers (it's hard to believe a Catholic could ever fall that far)! It's nothing short of scandalous, and the only thing that is more scandalous is that some people believe it!
Matthew 5:17
"Do not think that I have come to abolish the Law or the Prophets; I have not come to abolish them but to fulfill them.