There's a story about a man named Samsundar Balgobin who won first place in an international linguistics competition with his response to following challenge: "No English dictionary can adequately explain the difference between 'complete' and 'finished.' How would you explain the difference?"
This was Mr. Balgobin's response:
When a man marries the right woman, he is complete.
When he marries the wrong woman, he is finished.
As the story goes, his answer earned him a five minute standing ovation, he was rewarded a trip around the world, and he was invited to dine with the Queen of England. No doubt the judges themselves were married, and knew firsthand just how accurate is this definition.
From a theological perspective, there's also a difference between the two words. When Jesus cried out on the cross, "It is finished!" he was saying, in effect, "The power of sin is done away with. It is paid in full. It is gone forever. It cannot hurt you anymore."
And when Paul said, "Ye are complete in him," he was saying that the Jesus you received at salvation is all you need for your life in God. You have complete forgiveness in him. Your hope is complete. Your future is complete. Your purpose is complete. In him you have everything and lack nothing.
With Jesus, you're complete and sin is finished.
Without him, we're all finished.