Neither the reality of a single night nor even of a person's entire life can be equated with the full truth about his innermost being (pg. 98). This quote seeks to shed light on how Fridolin and Albertine's seemingly happy marriage to the outside world had become so mundane and lacking in passion that to add some sense of excitement and variety they choose to reveal their secret sexual fantasies.
As they listen to each other's fantasies, feelings of insecurities and betrayals surface. They both admit that for one night of passion in their fantasies they are willing and ready to give up everything in their lives. Fridolin feels so betrayed and angry that he leaves the house ostensibly to visit with the family of a patient who has just died. However, instead of doing this he wanders the street looking for actual sexual encounters, which he actually never consummates.
In the end he confesses what he has been up to when upon returning home, he finds his wife sleeping with the mask he wore to an orgy the night before, on the pillow beside her. Albertine listens quietly, comforts him, assuaging his guilt, and agreeing to let bygones be bygones. They move on with their lives pledging to be faitful and glad that they had survived this bump in their marriage's path. Fridolin verbalizes the aforementioned quote, which in essence really states that what we see as the outward trappings or appearances of a person's life does not really represent the entirety of an individual's life. There is a lot that lies below the surface of what is actually visible to the observer. I chose this quote because it represents what is the reality of human life. What we see outside is sometimes a far cry from what is actually the innermost reality.