Jesus said to him, "If you would be perfect, go and sell all that you have and follow me."
The goal isn't good by earthly standards, the goal is perfection.
There are only two ways to be perfect. Never sin or be forgiven. And God said there are none righteous so the first one don't count.
Actually, the greek for "perfect" in the Bible has a lot of different meanings. katartizo means "mended or made fit" while teleioi means to "finish or fulfill".
I like this example of the "perfection" principle:
Heb 6:1-6 MKJV
(1) Therefore, having left the discourse of the beginning of Christ, let us go on to **full growth**, not laying again the foundation of repentance from dead works, and of faith toward God,
(2) of the baptisms, of doctrine, and of laying on of hands, and of resurrection of the dead, and of eternal judgment.
(3) And this we will do, if God permits.
(4) For it is impossible for those who were once enlightened, and have tasted of the heavenly gift, and were made partakers of the Holy Spirit,
(5) and have tasted the good Word of God and the powers of the world to come,
(6) and who have fallen away; it is impossible, I say, to renew them again to repentance, since they crucify the Son of God afresh to themselves and put Him to an open shame.