I believe the most important thing we can do in life is develop our inner potential. I don't see why Christians tear people down by telling them they're sinful and worthless. You ought to encourage them instead to look within themselves and strive to reach their full potential.
I’m sorry if you’ve gotten the impression that Christians believe we are worthless—because the opposite is the case! Instead, we are so valuable in God’s eyes that He sent His Son into the world to give His life for our salvation. Would He have done that if we were worthless?
At the same time, we will never become the people God wants us to be by looking only within ourselves. When we do that (as you are suggesting), we ignore God and think we can solve all our problems on our own. We become centered instead only on ourselves, and in our pride we put ourselves in the place of God. We end up denying our weaknesses and our selfish motives, and we have no real answer for our feelings of guilt or failure.
Most of all, looking only within ourselves means we overlook our greatest need: to be reconciled to God. God made you, and life’s greatest joy comes from knowing Him and discovering His plan for our lives. It comes also as we discover the gifts and abilities He has given us, and begin using them for His glory. Nothing is greater than reaching God’s potential for your life.
Don’t turn your back on Christ. Face instead your need for His forgiveness and grace, and open your heart and life to His love and His transforming power. The Bible says, “Do not conform to the pattern of this world, but be transformed by the renewing of your mind” (Romans 12:2).