How can you be perfect?
Mt. 5:48 says
Be ye therefore perfect, even as your Father which is in heaven is perfect.
This was a statement or command by Christ, so He must have expected us to fulfill it. But how is the question.
First, we have an inherent sin nature inherited from our fathers that we cannot shake. It is what separates us from God. You can't get to heaven by living good, as you can never overcome that basic sin nature on your own, even if you try very, very hard. Any sin, from the smallest to the biggest, is proof that that sin nature is there. Nobody gets by without committing some sin - whether it is a simple "white" lie (Rev. 21:6-8) or some basic failure in character - lust of the eyes - lust of the flesh - pride of life - or something else (1 Jn. 2:16). They're all the same in God's eyes.
So what can we do? Well, one of the Holy Spirit's operations is to direct our path. The closer we get to God, the better we are able to hear and feel the moving of the Holy Spirit and if we are obedient to what the Holy Spirit tells us to do, we will not sin any further. Don't give in to temptations (1 Cor. 10:13; Jas. 1:12-16). It doesn't remove our need to accept Christ as our Savior, but with God's help we can live as God expects us to live.