纸张的反面

reverse side of the paper

反面缝着商标

brand stitched on the back

事物的反面

negative side of things

反面教员

someone who sets a negative example

反面教材

warning example

反面经验

negative experience

反面教训

lesson

起反面作用

play a negative role

反面意见

opposing opinion

反面理由

reasoning against something

不但要看问题的正面，还要看问题的反面。

It is necessary to look at both sides of the problem.