It can be and is very frustrating when trying to witness to a non-believer, (btw did you know the word “witness” in New Testament Greek means “martyr”?) So not surprisingly it is not too difficult to see that getting through to them is hard. A Bible scripture I find encouraging is found in the Book of Romans:
Romans 8: 5-7 (NASB)
5 For those who are according to the flesh set their minds on the things of the flesh, but those who are according to the Spirit, the things of the Spirit. 6 For the mind set on the flesh is death, but the mind set on the Spirit is life and peace, 7 because the mind set on the flesh is hostile toward God; for it does not subject itself to the law of God, for it is not even able to do so, 8 and those who are in the flesh cannot please God.
Keep strong in your witness no matter how much you want to pull out your hair!