Every day of our lives, we are surrounded by promises. Now, I'm not saying you'll hear the words "I promise..." multiple times each day. Rather, what I am saying is that there are so many things, people, situations around us that will promise true joy. In the advent of the Netflix era, I've become used to being able to watch television without being bombarded by commercials (though I suffer through it in YouTube). However I remember, back before Netflix was a thing, that watching Saturday morning SpongeBob meant you'd be blasted with commercials advertising you this and that. Perhaps it was a bag of goldfish that promised to make you smile, or maybe it was a can of Chef Boyardee that promised to journey far and wide just to be in your bowl. Whatever it was, promises were constantly being made to me through my television. And though many of us pay streaming services like Netflix to remove commercials from that equation, it doesn't change the simple fact that every day we are surrounded by promises.
The chief of all false promises has to do with joy. In fact, all false promises touch upon this very idea. Though, before we can properly understand a false promise, we must understand a true promise. The true promise is this, in God alone will we find true joy. I take this from the first question of the Westminster catechisms ("the chief end of man is to glorify God and enjoy him forever"). You see, our joy is found when we are going with the grain of what our ultimate purpose is. One does not find true and lasting joy in that which is not according to their ultimate purpose. It's backwards, it makes no sense. However, if it is the case that only in God will we find true joy, then all that coincides with that is not a false promise but a true one.
Consider Psalm 37:4, "Delight yourself in the LORD, and he will give you the desires of your heart." Without this proper understanding of the one true promise, this seems a bit backwards. Doesn't James 1:13-15 seem to tell us that our desires sinful and not pleasing to the Lord? Indeed they are... when not first reordered according to the Lord and by the work of the Spirit in our hearts reordering our affections. If the Spirit does not reorder our desires (or as John Piper says, "change our taste") then it would be sin for God to grant us our desires. Yet, if the Spirit has reordered our desires, God can certainly grant us our desires since we have first and foremost delighted ourselves in the Lord (that is, we have understood that in God alone we will find true joy). This understanding of the true promise then helps us understand the false one.
The false promise is this, in [insert anything that is not God] will we find true joy. Notice that it is not merely the removal of "God" that differs the false promise from the true one. I have also endeavored to remove the "only". That is not to say that a person could hypothetically affirm the statement, "In sex alone will we find true joy". In fact, I am certain many people have affirmed such a statement. Rather, the removal of "only" in understanding the false promise is that it allows it to comfortably exist within the framework that sees God as one of many means things by which true joy is found. The true promise does not merely say that in God will we find true joy, the true promise is that in God alone will we find true joy.
This false promise thus takes many forms: "in academic performance will we find true joy", "in successful children will we find true joy, "in the heavenly reunion of deceased loved ones will we find true joy". These are all iterations of the chief false promise. God responds with a resounding NO! (See 2 Kings 18-19 with Sennacherib making a false promise to Hezekiah and the Lord responding) That is not to say that academic performance, successful children, and the heavenly reunion of deceased loved ones are wrong things for us to take delight in but it should be a delight that is subservient to the chief one which is God himself. We can take delight in things, people, and situations as a means by which we direct our ultimate joy and delight in God himself.
Finding ultimate joy in anything but God is contrary to our very purpose which is to glorify and enjoy God forever. Thus, it will never satisfy. A horse kept in an enclosure for years upon years will never be satisfied because nothing they do can be directed toward their ultimate desire... to run. So it is with us. If our joys and desires are not ultimately found in God himself, we will never be satisfied.