Sometimes one of you makes a clicking noise in the back of your throat when you sleep, not allowing the other member of the marriage to fall asleep.
Sometimes one person is much worse at keeping secrets than the other.
Sometimes one person just can't seem to find the motivation to clear off all the junk on top of her dresser and it just sits there forever looking so very untidy.
Sometimes you've been in out of town for a week and are so ready to come home that you become irritaty and complainy and restless.
Sometimes the air conditioner stops working and you're left to sleep through an arid Arizona night and swelter in the heat of day for 30 minutes before saying "FORGET IT" and driving up to your parents house for the weekend.
But other times marriage is easy.
Like when you come home from Louisville to find that the other person bought all the snacks you mentioned wanting on the phone the other day.
And snacks are so much more important than a clicking noise anyway.