if you are using a ballot in which everyone can see, and you vote for this man and some body looks over and saw who you voted for and he does not like that, he could get up and start yelling at you, and maybe start even hurting you because he did not like the man you voted for.
if you are using a secret ballot no one can see who you are voting for one no one would know.
i hope that and if you need i can explain better : )