1. Often times Christians are guilty of putting a lot emphasis on what the person has to do. In other words, the Bible is clear that we are to repent and believe the gospel. The Bible is clear that we are to bear fruit. The Bible makes it clear that we are to persevere in our faith to the end. The Bible makes it clear that we must place all of our trust in the finished work of Jesus Christ. However, at the risk of missing other Scriptures there is too much placed into the hands of the created.
2. But there are some who sometimes fall to the other side. What I mean is that there are some who falsely understand God's grace and God's sovereignty to mean that there is not responsibility of man. In this situation people miss the point of works that belongs to the created.
I think those are extremes and most people I know fall in between those. But you understand my point. Here is the predicament we sometimes find ourselves in. We are to work out our own salvation with fear and trembling. Let us never forget that the Christian life is a life of hard work. We must discipline ourselves for the purpose of godliness. And yet, we will fail! So we must never forget that as we work out our own salvation with fear and trembling, it is God who is at work both to will and to work for his good pleasure.
Now back to Philippians 1:6. The reason Paul could say that he was sure that he who began a good work would complete it is two-fold. First of all, when God starts something He will finish it...period! Salvation begins with God. Jesus is building His church. The first convert in Philippi was Lydia and the Bible is clear that she is saved because God opened her heart to believe. All of this is because God starts it, so it is easy to see that God will finish it. On the other side of that, Paul can be confident because those in Philippi have given evidence of God's work in their life. The church has now grown and the believers have rallied together to send gifts to the apostle Paul. They are demonstrating their love for both God and neighbor in the way they act and the deeds they do. So Paul can be confident that God has begun this work because he can see the works in their lives.
So where is your confidence? If you have faith, without works, that faith is dead (nonexistent). And if you have works, without faith, they accomplish nothing. Work hard in all that you do that you might glorify God with your life, but never ever ever put your confidence in anything other than God who is at work within you.