Do you find it challenging to keep a promise? No, it is easy. I always promise what is in my power to fulfill.
What is the biggest reason why you break your promises? That's easy too. If a person treats me ( or I found out something about him/her that is all together downright screaming awful) utterly wrong, terrible or harmful, I will not hesitate to turn my back and never think about that person ever again. Also, if I keep my side of a promise and a person on the other side is not, then there was no deal in the first place.