Nervousness is less obvious than they think.

In a 2003 Journal of Experimental Social Psychology (Vol. 39, No. 6) study, Savitksy took students who were nervous about public speaking and told them the truth: Their nervousness is less obvious than they think. In the end, observers didn't notice their nervousness, and the students gave better speeches compared with a second group that received no instructions. "People are sometimes nervous over the possibility that they will look nervous--and the fear that their nervousness is apparent serves only to make them even more nervous," Savitsky says. "By telling them about our previous findings, we cut through that cycle. It's possible to get around these fears. I think that's cause for optimism. Yet I find I still overestimate how much others will notice my behavior, and I do this research. So some portion of it is inescapable."

Just a quote from reading some articles.