Throw any two people together, add the ineluctable ups and downs and stir the mixture vigorously with a spice of personality differences, time and money problems and viola, you will have a picture of what reality in relationships is. A few to stormy arguments may arise. Good if the bickering would end equally fast as how quickly it started. But what if it does not? What if each party refuses to give in?
Marriage is a more complicated thing. Although it entails promises of endless felicity and romance, that is not always the case. When you spend almost every day of your life with a single person, you tend to know that person deeper and you eventually notice every awful bit there is. Time is also a factor. Although over familiarity is good because you already feel confident with each other, it could at some point lose the excitement and dull the relationship over time.