“If perfection is impossible in this life, why did Jesus tell people to go and sin no more?”
Jesus actually did this twice, and both accounts were preserved for us by John, one in chapter 5 of his gospel, and the other in chapter 8. In my Bible, the latter narrative comes with a disclaimer to the effect that the earliest manuscripts of John’s gospel do not include it, which, frankly, doesn’t bother me a whole lot. I have always loved the story of the woman “taken” in adultery. It portrays the Lord in a way that seems to me wholly consistent with his revealed character. I believe John wrote it and that it is God-breathed just like the rest of his gospel.
Still, opinions vary about that passage. If you discount it, then you only have to answer this question once.