Well the question posed is entirely subjective and depends on umpteen variables, the most important being do the two people in the marriage have enough of the right stuff to take them through life's path together. Once upon a time separation wasn't an option largely because of financial constraints and society's attitudes. Now I believe something in the order of 50% of relationships founder, maybe before they've reached that deeper stage that hopefully evolves in longer lived partnerships of contentment and an acceptance of each others foibles. I know of at least two married couples who have survived into a happier stage in later life, only due to the extreme tolerance of one of the partners in the marriage. Long lasting happy marriages are imo something to be lauded in this day and age of throw away everything. I think I was moved when I read about Jack Dromy's recent death because my gut feeling, and of course I can't know, but I imagine, that was a happy and long lived marriage sometimes couples exude that quietly, not in an over the top public declaration of love that so many well known faces put out there into the public domain these days. When I felt sad for Harriet Harman I guess I was feeling sad in projecting myself into that loss of a deeply loved partner.
Maybe we are shaped by our earliest experiences of marriage, which would be that of our parents. My parents were catholics so divorce wasn't something they would have contemplated, but the extreme tolerance of my mother was what carried them through and although my father , a difficult and irascible individual, appreciated her much towards the end of his life, most of their marriage he took her for granted. I think that from an early age I had a subliminal feeling that being taken for granted wasn't something I wanted from a relationship.
I think there has to be a lot more to underpin an initial attraction, kindness, humour, conversation, mutual appreciation, not having vastly differing attitudes to raising children or money and tolerance are all pretty important components to getting along. So to address the original point, are all marriage are hard work, well some will be and if they are too much in the way of the hard work variety then they probably won't last. Particularly as there will be the stresses of children, extended family, bereavements, money, working lives, where a mutual support has to be there. Ideally, though no they shouldn't be massively hard work, sometimes maybe, but for most of the time no, but again that's down to the person one marries and an ability on both sides to understand each other.
