Maybe the author was implying that a lovers relationship where one party is still hopelessly in love with another and is forcing himself to stay in a relationship because it is convenient and more acceptable wouldn't last long. Also, a relationship that begun with insincere and wrong intentions is not likely to last long. There may be no fights but it doesn't mean they will be genuinely happy together.
Also, even the strongest loves that have lasted decades have had their fair share of fighting/ disagreements but they learnt and grew from them.
where did they say that??
Wait did I read that right? Did the author just imply a relationship without fighting/disagreements wouldn't last? Um okay....