What is the "secret" to understanding non-duality?

I know for sure that I have a front & a back. They are one as far as being me but I can't have one without the other. I know when I see someone do something I hate it is something I am doing or going to do or capable of doing even though I think I am above that....years ago, I was a great money manager...I had someone who owed me money & she had the money & I thought she was dispicable...actually, I still do but she died last week....so I am wondering now that I owe money to people why I choice to put them off so I can do what I want. I have excuses such as I have to care for myself or I am no good to others. So I think we are all probably not about to accept everyone & everything unless we get some kind of understanding which comes through life experience. So I could tell you that the secret is just being understanding but do any of us have complete understanding.....I have had the Westboro Baptist church come to my state to protest funerals.....I do not understand these people, I do not want to understand them so I accept that I would rather be angry with them even though I do understand 99% of what I see in life. I have a friend who is a republican & chooses to be miserable....I was like that when I was younger but he can come out of that muck & I don't want to go into it to be one with where he is at but it would be easy to say he needs to learn from where he is at just as I did. So the secret is putting ourself in the others place but I would rather stay in the votex of peace, joy, love, laughter, harmony , balance, all that is good so when the other stuff comes up I call it contrast & just ask myself what I prefer & go to that instead of trying to get into the ugliness.