Although the foregoing comments on male fear are probably true for some (being laughed at!) my own experience is taht primarily you dance with someone because its an enjoyable experience for both - if you can keep time. When concentration or nerves get in the way it ain't pleasant for either partner and for the man who's trying to impress the odd's are he probably thinks its better not to begin than to loose it one more time. Just like performing it takes practice to give confidence - but how do you practice?