Short version:
To carefully judge a new love interest against a current spouse, and make a wise judgment about who is preferable, requires a great deal of time and attention. However, single people pledge eternal love very quickly, even though their knowledge can be no more complete.
Expanded version:
Consider a man with a loving family, who has been married to his wife for no less than two decades. He is content, he has a good job, and his children have good prospects. He never fights with his wife. But, like every man, he knows there is more that could be attained. It is only natural to think that life would be even more pleasant if his wife had more skill with rhetoric, or a greater interest in ancient history, or liked to play tennis. But it is a virtue to remain content, and not be distressed by unavailable possibilities.
This man meets a new woman, who is lovely, and witty, and kind, and shares with him some qualities, interests, hobbies, and virtues that his wife does not share. He is intrigued, and starts to fall in love with her, and wonders if his life would be better with her. At this point a wise reader will object that the man proposes a most abrupt and immoderate change, and disaster is the likely outcome. But let us put aside any qualms about sudden, large changes, and consider another argument.
To decide in favor of the new woman, and to leave his family, the man must, in his best judgment, be confident he will be happier with her, and have a better life. He must know her flaws, to be certain he will not find them more loathsome than his wife's flaws. He must know her assets, to be certain they are greater than his wife's. He must know her interests and hobbies, to be sure he prefers them, and will not be giving up some most important ones. He must spend time with her, to see what she is like after the initial infatuation wears off. He must also see her in all manner of situations: when she is angry, when she is sad, when she is happy, when she is anxious, when she is scared; in this way, he will immunise himself to the possibility of a hidden flaw in her disposition that could cause him great grief. A sagacious reader will see the great weight of tasks necessary for the man to pass a considered judgment, and will see they must, to be done properly, take a great period of time.
Let us now consider a single man, who is a young adult. He has no family, but he hopes to have one soon. He meets a woman, and quickly falls in love with her, and they marry. It is a common story. But why should this young man have any better judgment, or faster wit, than the family man we considered first? All the considerations the family man needed to make about his new potential wife, so too a young man should make them about a potential wife, if he wishes to avoid mishap. Some have said the young man has less to lose, and it is acceptable for him to assume a greater risk. But he risks his future family, which he should value no less than the family man values his own family. And so he must exercise equal prudence and caution before embarking on such a great commitment.