Rebellion is likened to witchcraft. No one will readily want to engage in practices of witchcraft, however when we operate in rebellion we equate to this grave sin. In Jeremiah God said that His people committed two grave sins. They have forsaken the Lord and turned to serve idols. Serving idols is like witchcraft. Lucifer walked in rebellion before God and was thrown out of the heavenlies. Rebellion first starts in the heart. The issues of life flow from the heart. Obedience starts from the heart as what is spoken from the mouth proceeds from the heart.That is why God looks at the inside.
Rebellious people always have an alibi. They would justify any wrongdoing. In this case, Saul blamed the soldiers for bringing in the spoils. He also justified that the cattle was for sacrifice to the Lord. One one has a sound justification, one can become pretty arrogant in ones approach.
We sometimes cannot even know the condition of our own hearts. Jer 17:9 The heart is desperately wicked above all things, who can know it. That is why we need the HOLY SPIRIT to guide us into all truth. Being humble and accepting that we are fallable will enable us to receive God's grace for change. Grace comes to the humble. Repentence and prayer can rid us off such rebellion.
I believe that sin left unattended can grow. May start off as a serpent in Genesis and become a Dragon in Revelation. We are commanded to work out our salvation with fear and trembling. Where sin abounds God cannot use us as a vessel for His service.
I also like to add this additional information. Samuel was anointed with a FLASK of oil. Flask made with human hands. David was anointed with a HORN of oil. Took an animal to be killed (sacrifice) so that he culd be anointed.