There are few things acquired that cause a person to say, "I don't want anymore." Yes, perhaps for a short time you are satisfied, but it doesn't last. You play on a team and they win the championship. It's enjoyable for several days, but by next season you want that trophy once more. You work out and gain muscle, but you only have to look at the guy benching 50 pounds more than you before saying, "I want to get bigger." You buy a rod and reel and a little tackle, but you don't have to fish too many months before you are purchasing even more lures, more poles and a boat. We want something more and something better.
Now some would say this is a bad thing. We're supposed to "be content in all situations" (Philippians 4:11). But Paul is talking there about a situation he was placed into. He had some troubles and learned to live with it and honor God while going through those things. We are to glorify God no matter the situation. That's what Paul was saying. But that verse simply doesn't transfer to being content with our spiritual lives. Many times you and I are satisfied with honoring God some times or at the 'right' times. We're like ones who gain a victory in the season without desiring another win. No team will last long if they don't want to win. God desires for us to win spiritually and you and I should desire the same.