These 72 neophytes returned from their mission full of joy and enthusiasm. Obeying those instructions increased their level of courage and confidence to serve which always results in an increase of personal fulfillment. The Personal Commission of Jesus Gives us Courage and Confidence. Often the manner in which we perform a task is determined by who it is that asked us to do the task. For example, if Bill invited me to write a 250 word editorial for the bulletin I would seek to do a good job.
Many people have a low level of confidence and courage because they have never tested their limits.
Fear of failure has kept them from testing their limits. You'll never know what you can do until you try and fail. Without failure you'll never reach your potential. And if you fail to achieve your God given potential your level of boredom and discontent rises. Part of the reason he could speak those bold words is because his faith had been tested by nasty persecution.