Romans 7
13 Has then what is good become death to me? Certainly not! But sin, that it might appear sin, was producing death in me through what is good, so that sin through the commandment might become exceedingly sinful.

We need sin to appear sin, because it always wants to hide in us and conceal its true depths and strength. “This is one of the most deplorable results of sin. It injures us most by taking from us the capacity to know how much we are injured. It undermines the man’s constitution, and yet leads him to boast of unfailing health; it beggars him, and tells him he is rich; it strips him, and makes him glory in his fancied robes.” (Spurgeon)

Without the law, you cannot know if you are sinning or not. So you could have been hurting yourself and not known it.
This is how I read this.