be afraid to do sth.真正的意思是“害怕做某事”,也就是主语对做某事内心感到恐惧;be afraid of doing sth.表示主语内心里不情愿做某事,也可以说是不希望发生某事,但自己不一定能避免它.例如:
He was afraid to go out alone at night.(他害怕晚上独自外出.暗含的意思是“他对于晚上独自外出缺乏安全感”.)
He came late to school and was afraid of being scolded by the teacher.(他上学迟到了,害怕被老师吵.暗含的意思是“他不情愿被老师吵”.)