1) Ungrateful people are sour and miserable to be around. They are completely self centered in the worst sense of the word. They are, therefore, horrible witnesses for Christ and his selfless act of saving a lost and broken world.
2) Ungrateful people are susceptable to the self loathing and mental fragility that leads to all manner of internal turmoil. There really is something to that "stop and smell the roses" thing! If the enemy of your soul can confuse you, you will lose the vision that your life has purpose for God's kingdom.
3) Ungrateful people are so completely self absorbed that they are not pleasant to be around. If we fall prey to ingratitude we find ourselves alone- and in that place we can do little damage to the kingdoms of Hell and much damage to self.
4) Ungrateful people are easy prey to doubt and unbelief. They spend little time examining their own life (if they did they would realize the mercy that God has given them). Someone has once remarked that the unexamined life is not worth living. Certainly that is doubly so for the ungrateful.
5) Ungrateful people have poisoned souls. They are toxic in their poisonous negativity. Grinding down even the most cheery person and offending those that are looking for spirituality. Most people run from their malevolent poison, and those that don't, wish they did.
So refuse ingratitude and embrace a lifestyle of thanksgiving. 1 Thess 5.16b "...in every circumstance give thanks, for this is the will of God."
Choose 5 things to be grateful for this day. And tell someone how thankful you are!