Well, maybe not "Relationships with intense difficulty", but it's a very common and very naive assumption that the perfect person for you will "just work" and there will be no fights and no difficulty. Loving someone is a lot of hard work - and it's extremely rewarding. Teenage relationships where everything "just works" and everyone is in bliss tend to end with a lot of tears.

Anyways, yes, it's not a set-in-stone rule - but typically, anything that's extremely easy also has a disappointing side. The best stuff in life takes work.