They are like the beaten down path. No matter how good your message is it is like throwing seed on a sidewalk. It just sits there. Soon it disappears. It doesn't really get down in and start to grow.
Some people listen with shallow hearts.
They like what you say for a while, but after a while some little thing happens to them, they go through some rocky times, and their tiny, fragile faith is shattered. They never really throw themselves into God's Word, and so, when the going gets rough in their lives, they throw out God's Word. A third group of people will listen with crowded hearts. Chances are they will keep coming back and listening to you. But their lives won't change all that much.