Let me explain.
When a person is born again, the Holy Spirit of God baptizes their human spirit in His Presence. The end result of this is that the Holy Spirit can speak to my human spirit any time, any where.
When the Holy Spirit speaks to my human spirit, the information my spirit is receiving is shared with my human soul. Here is where the problem begins because my human soul is easily confused, it can be distracted and deceived. When the Holy Spirit uses His Presence to speak to my soul, my soul can choose to ignore what the Holy Spirit is trying to say.
This is where Satan comes into the picture; Satan is always trying to put pressure on our lives to make listening to what the Holy Spirit is saying hard to accept. Discipleship involves living in community with people who have more experience than you do bearing the burden Satan crreates to make us disobedient to the Holy Spirit.
The end result of this struggle affects our human bodies: it reveals itself in how we treat other people. So when you hear reports of people who compromised their faith in some way and became a moral failure, what happened was the person whose faith was compromised stopped listening to what their spirit was being told by the Holy Spirit, and Satan was able to move in and take over their lives.
Now that I have gone into great detail to explain clearly and simply what happens in an individual person's life, we should consider if one-on-one discipleship is a good idea. The answer to that is no.
Let me explain why. There are many places in the world where it would be better to share your faith with your friend, his wife, his parents, her parents and all of their living relatives. This is important because in many places it is considered wise to ask people who are older for help thinking about these kinds of choices because they have more experience in life. The collective group might see something an individual could overlook or misunderstand.
So when you want to reach out to people, include as much of their family and as many of their neighbors as you can, so that the person you want to reach and the people he or she has to share life with after they are reached can believe on the Lord Jesus Christ and be saved together.