That is an instinctive, reflex action. Whenever the mind hears something that it does not want to hear it automatically closes its door. To shut the mind to truth we do not want to hear is the straight road to disaster and to tragedy. If so, the fruit is obviously not there own salvation. Every believer bears SOME fruit.
Every believer is a witness.
Every believer bears the fruit of a changed life. When applied to the lost, this truth means we must tailor our methods, taking the heart of the believer into account. It also means we can take heart in our efforts at witnessing. That is how the disciples were feeling, when they saw Jesus banished from their synagogue and regarded with suspicion. In many places His message seemed to have failed, and they were discouraged and downhearted.