Jesus spoke of people who hear the Word of God, but it never quite takes root. These people appear to be converted and even motivated. They seem to be living on an emotional high and even try to bring others to Christ. Yet they are a picture of soil embedded with rocks. The good seed of God's Word breaks ground and shoots up, but no fruit ever appears. No real change ever results. Theirs was not a true encounter with God.
Why did they fall away? It's possible they built their faith on the wrong foundation. Maybe they responded to the gospel because a friend of theirs did. But conversion is not a group effort; you have to make your own commitment to Jesus. Another possibility may be that unbelief set in, causing them to begin doubting God at their first emotional low. Or, they gave up at the first sign of persecution for the gospel's sake.
If you are a true follower of Jesus, there will be hardships, times of trial, and seasons when you don't feel as though God is near you. And there will be times when people give you a hard time for no other reason than the fact that you say you are a Christian. So don't build your life on a friend's example or approval. Don't even build it on a church. Build it on Christ.