Do we rationalize our sins?

An example of how King Saul rationalize his sins when confronted by Samuel: 1 Samuel 15 20 And Saul said unto Samuel, Yea, I have obeyed the voice of the Lord, and have gone the way which the Lord sent me, and have brought Agag the king of Amalek, and have utterly destroyed the Amalekites. 21 But the people took of the spoil, sheep and oxen, the chief of the things which should have been utterly destroyed, to sacrifice unto theLord thy God in Gilgal.  -kjv 20 “But I did obey the Lord,” Saul said. “I went on the mission the Lordassigned me. I completely destroyed the Amalekites and brought back Agag their king. 21 The soldiers took sheep and cattle from the plunder, the best of what was devoted to God, in order to sacrifice them to theLord your God at Gilgal.”  -niv 20 “But I did obey the Lord!” Saul answered. “I went on the mission theLord gave me: I brought back Agag, king of Amalek, and I completely destroyed the Amalekites. 21 The troops took sheep and cattle from the plunder—the best of what was set apart for destruction—to sacrifice to the Lord your God at Gilgal.”  -hcsb Observations and comments: 1)  The context of the verse was when King Saul was told by the Lord through Samuel to totally annihilate the amalekites. 2) However, Saul saved the best of the cattles and claimed to have done that to sacrifice them to the Lord.  Saul obeyed the Lord partially and rationalize his sins as in 1 Samuel 15:20 when confronted by Samuel. 3) Do we rationalize our own sins or do we completely repent of our sins when we become conscious of it?