Ummm, it's mostly to do with the year, month and day compatibility.

However, another big factor is the balance of elements. We're all affected by the energies of the earth around us consisting of Water, Fire, Metal (ore in rocks), Earth and Wood.

If this guy has the same type of elemental balance as you, then you'll both find each other incompatible over time.

There is a hell of a lot to learn about Chinese Astrology and how it all makes sense. None of it is romantic hocus pocus, it's all genuine science that the Chinese have learnt from long long ago.

I have two colleagues in work. The guy is year of the horse and the girl is year of the rat. There is always some tension between the two that I can detect as discomfort.

Married now for 15 years mental rat and fire horse.
Wow, I would have to agree to disagree,
I am a mental rat and my wife is a Fire Horse. What makes this relationship really work in a practical sense is teamwork, compasion for humanity and a center that is more important than self "God" or what ever you may call it, art and cultural events help too along with beauty and a passion for the good things in life.

Business:
We have finally found a common ground in a work capacity and soon we will have a business of our own. Rats need to learn not to get the horses hooves entangled in critical thinking and scheming they don't want to hear it!,so find and ear that will listen. This probably won't happen because
rats are usually looking at the big picture. I can't tell you how many funny looks I have gotten over the years from people when I tell tem about my Ideas. They are the same looks that my wife’s gives in other word Rat JUST GO DO IT!. And the horse will gallup and applaud and telling everyone that it was really there idea all along, we just have to quietly except this and move on to the next big idea,"Don’t worry" we have a bevy of them they are like water to us. Just watch the bank account and at the end of the day you be glad that the spark is still there and it will always be passionate and intense.
Look around you and you will see that so many other couples over the year just don’t have the spark and edge that this relationship has “its worth it”.