Okay I thought about this a while ago, but forgot to post it.
I figured out the two questions you should know the answer to when you are trying to figure out whether or not you should marry them:
1. Which way they tilt their head when they kiss.
2. Whether they like the toilet paper coming off in front of the roll or behind.
If your answers match, then you are definitely compatible. Okay there is a lot more to it than that, but I think those are two essential things. I know I could never be with someone who answers even one of those differently than I do.