As a psychologist, I have known of world-class devastating marriages and divorces, experiences too improbable for a novel, lived by people who felt that personality doesn't matter in a relationship if there is attraction to each other. Emotional immaturity and impulsivity are key warning signs, as are a history of abusive relationships and lacking independence from parents.
But it can take time to know someone too. In 1930s Vienna, before an unmarried American psychiatrist departed after completing his training analysis, Freud said he hoped the doctor had the good fortune to achieve a happy marriage. "Does one need luck with all your psychological knowledge?" the doctor asked, and Freud replied, "Of course, for only after living with someone for a long time does one really know them."