Christians sin just like everyone else.  They just, hopefully, learn from it and use it to get closer to God.  I've known many Christians who struggle with their sin, be it alcoholism or infidelity or whatever.  The goal of Christianity is to convict the heart to make a change. What is more a cause for celebration?  Someone who sins but learns and turns away from their sin or someone who just behaves because they have never struggled with temptation?