The meaning of this sentence is that humans are very complex creatures with many sides. Sometimes it is difficult for you to see through them, and it is even harder for others to see through them.

Sometimes we really can’t see ourselves clearly, which may prevent others from truly understanding us. Take myself as an example. In fact, I value my friends very much. As long as they are my friends, no matter what the matter is, I will be willing to help them and stand on their side. I cannot allow others to call me friends. No.

However, many people who don’t have a close relationship with me will say that I have a rather cold personality and that I seem to be a very cold person. I think most of the time I just don't know how to take the initiative to communicate with people. Maybe the side I show is not the side I know in my heart.

So, everyone should be multi-faceted, but it is difficult for us to see through ourselves, and it is really difficult for others to fully understand you.