Some dont really have limits. When my wife and I had our stupid little talk with an elder before we were married. He told us that oral was a up to the couple (hot damn!!! I thought) and anal was out. Well, happily this couple was ok with one of those things and I'm getting hints the other might be ok too!! But yes, many of them must be terribly unhappy in bad.
"Honey, I want to make love tonight. Only because it's in the bible that we should".
"Ok, but only because I'm not supposed to withhold your marriage due".
"I'll turn the lights out before we get undressed"
"Who's getting undressed?"
After 3.5 minutes..........
"Thank you. That was quite satisfactory."
"You are welcome. I'll mark on the calendar that we did the deed so there is a record of our marital dues being taken care of."
"Hey next time, can you be on top?"
"What does the Reasoning Book say on this topic?"