Usually, we think of these people as just being lucky but it's really not a matter of luck. Those with easy marriages tend to have easy (going) personalities. They share the same traits:
*easy-going
*tolerant
*patient
*accepting
*un-controlling
*happy
On the other hand, you never know what going on behind closed doors. Everyone thought my uncle and aunt had the perfect marriage because they were always so nice. Married for over 50 years. But after he died, all the skeletons came out of the closet. I'll keep their secrets but suffice it to say, you never know the truth about another person's marriage so don't compare yours with anyone else's.
If your marriage isn't perfect or easy, ask yourself why. Mine isn't but it is quickly becoming so because I finally get that I have a lot of influence in my marital happiness. The happier, more tolerant, patient, easy-going I become, the easier my marriage becomes.
