These causes of not witnessing are from Richard Baxter's book, "The Saint's Everlasting Rest".
If we know the causes we may more easily overcome them.
1. One hindrance is sin. A person's own guilt makes him ashamed to witness. If a person is not excited about heavenly delights, why would he try to draw others enthusiastically to seek them?
2. Another hindrance is a secret lack of faith. If we truly believed that the unsaved would be eternally separated from God, how could we keep from speaking, or even avoid bursting into tears, when we look them in the face; especially when they are our dear friends? Were it not for this cursed unbelief, our own and our neighbors' souls would benefit from more active witnessing.
3.A lack of compassion is a further cause of neglect. Unlike the Good Samaritan, we pass by the wounded man. What difference does it make that the sinner, wounded by sin and enslaved by Satan, does not want your help? His misery cries aloud just the same. If God had not heard the cry of our misery before He heard the cry of our prayers, we would have stayed in sin's slavery ourselves. You will pray to God for the conversion of other people; why not talk to them about it, if you desire it? And if you do not desire it, why do you pray for it?
4. We are also hindered from witnessing by a desire to be popular. We are so eager to please people that it makes us neglect our duty to them. He is a foolish and unfaithful medical doctor who will let a sick man die for fear of troubling him. If our friends are mentally ill, we do not let them hurt themselves, even if stopping them causes them to dislike us. And yet when they are beside themselves so far as salvation is concerned, rushing madly on to damnation; we will not stop them for fear of displeasing them. How can we "love the praise of men more than the praise of God"? (John 12:43). If we "seek to please men, we shall not be the servants of Christ" (Gal. 1:10).
5.It is common to be hindered by sinful bashfulness. When we should shame men out of their sins, we are ourselves ashamed of our duty. Sinners do not blush to swear, be drunk, or neglect the worship of God; and yet we blush to talk with them about it. It is wrong to be shy in emergencies. Shall we be too bashful to shout, "Fire!" when we discover the auditorium is in flames? It is not a work to be ashamed of, to obey God in persuading people to turn from their sins to Christ.
6. A lazy and impatient spirit hinders us also. Sometimes witnessing makes people our enemies. Besides, it seldom succeeds instantly, but needs follow-up. Therefore we need patience. What if God had been as impatient with us as we are with others?
7. With many, pride is a hindrance. They would be glad to be the one who might lead a distinguished person to Christ, but they overlook the poor masses, as if the souls of all were not alike to God. These men fail to consider how low Christ stooped to us!