Lead Us to Life (1 Peter 5:8 (LD 52)

It is rather strange to ask the Lord not to lead us into temptation because we are sinners who follow our sinful desires quit well.  We also believe and affirm that God cannot sin.  If God cannot sin, and we are sinners why would we then ask the Lord not to lead us into temptation?  It seems that we are more than capable of finding and following temptation ourselves.  So, why do we pray such a request, and why even ask the Lord such a thing when really it is our call to walk the straight and narrow in Christ?  Right or is there more to this request?