This story is an example of how appearances can be deceiving - and how impressions and emotions can also be that way. Bertha is a young housewife who imagines herself happy. She is a comfortable home, a husband she respects, and friends that she enjoys. She finds happiness in even the smallest things. She imagines herself to be perfectly content.
However, Bertha allows the appearance of happiness to be deceiving to her own emotions. Because she has the "perfect" household, she assumes she must be perfectly happy. However, her marriage does not have passion and she is not close to either her daughter or those friends she so admires. She doesn't really know what is going on beneath the surface. She allows the picture to determine her gauge for her own feelings.
When she realizes that Harry is having an affair, the picture is shattered, and Bertha doesn't know what to do. If she can't trust the picture - like the pear tree - to tell her that she is happy, how will she know if she is?