The first Biblical example of someone caving in that comes to mind is Peter, his from fear of what the crowd might think of him the night Jesus was taken into custody. Peter showed remarkable cowardice. Fortunately he gained a ton of fortitude and made up for it on the day of Pentecost, when he spoke with boldness.
So what was the difference in these two circumstances? In the former, Peter left the disciples and faced the crowd alone. In the latter, he was with the twelve. What lesson do we learn from this?