It all depends on the approach. If everything was / is upfront then, like anything else it's a matter of constant communication. The biggest problem is that couples first marry for lust. I'm amazed how many cruisers or so called cruisers are on their 2nd or 3 marriage.
W/ and I started out with the understanding that we wanted to see the world and the most pragmatic way would be by a sailboat. Luckily we never bought one that would put us under (like a wooden 50' or something).
I can't say I agree w/ Jon's idea that you must LOVE sailing. My favorite point of sail is at anchor. LOL. However; we've had some really beautiful sails. That said however we've had some really crappy times at sea too. But no matter how you slice it; the good must out way the bad. The couple must like adventure. Each needs to understand that life is made up of stories and they only come by adversity. Who wants to hear what a great time you had with your significant other sitting in your den watching "The Big Bang Theory" in dual lazyboys with the room climate controled and mood lit! Not I.
But listen to some of Jon's breakages; Bernies fiction; Beth and Evans adventures, Roth, Hiscock, and the Pardey's. Those are fun and they almost always make may say "Gald it was them and not I".
Fair Winds