Protect Yourself or Another?

It seems that traveling allows for long periods of thought...sometimes good ideas come from this time, and sometimes I am forced to think about stuff I don't usually think about, or don't want to think about.
We were at a botanical garden the other day, enjoying the greenery when we witnessed a lone guy being beat up by a group of other guys. While it was happening, I was thinking that I was too far away to do anything, and even if I was closer, it wouldn't be safe for me to intervene...I wouldn't want to get hurt...But it got me wondering...when would I intervene? In this case I didn't know if the guy deserved it (hmmm, another line of thought for another day) or if the gang were just being bullies getting 'kicks'. I have heard that people are told not to be heroes in a situation like this because you can never know what other weapons are concealed...but it still left me with a feeling of helplessness, selfishness and caused me to question my willingness intervene and possibly prevent someone elses harm.