I know I am poly because I love more than one person. I know I can achieve a poly relationship because I am good at time management, being able to step away from one person to be with another and give them the same amount of undivided attention as the other loves I have. I am able to consider all my partners as being equally valuable and worthy of my respect, honest communication, love and attention sexually and otherwise.
that's pretty much it in a nut shell.
My husband is poly and he struggles with some of the above, that doesn't make him any less poly though... just more poly in theory and support... there is a difference. I don't know if he will always be the latter, but he is right now and is happy where he is at.