About the book "Wonder"

My name is August, by the way. I won't describe what I look like. Whatever you're thinking, it's probably worse.

I don't understand mean of the last sentence. Can you explain it to me?


I won't describe what I look like. Whatever you're thinking, it's probably worse.

The last sentence has to be taken in context with the previous one. The meaning is that however bad you can imagine their appearance to be, the reality is probably worse than that.