Nearly every flight instructor will tell you that checkride jitters are more to blame than any other factor when a student fails the private pilot checkride. Most examiners will tell you that many well-prepared students fail to perform as well as they might because of anxiety.
It is often said there is only one chance to make a good first impression. With a major AOPA 2010 study placing the overall student dropout rate at 70 to 80 percent, this is especially true for flight training.