My mother always stressed to her kids the power of a smile and the importance of not turning your back when you see someone being bullied.
When I was in middle school, I witnessed a teacher seriously bully a classmate with Tourette's syndrome. I asked the teacher to stop, but was told by that teacher that my classmate didn't need anyone to defend her! The abuse continued, so I took it up with my mom, who accompanied me to the principal's office and stood by my side as I recounted what my classmate had endured. Things changed at the school, and my classmate then had at least one class she could attend in peace.
Recently, my mom reminded me how proud she was of me that day. She pointed out that we may never know what else a person endures, but we shouldn't be the one to turn away. I'm still taking her advice all these years later.