Of Calisto, Celestina says,

There is nothing more proper to lovers than impatience; especially new ones. They never once think of the harm which the meat of their desire may occasion unto them and their servants.

This is a pretty ironic statement considering that Calisto's love for Melibea would have no terrible consequences except for his own misery, if it were for Sempronio's involvement of Celestina. In this quotation, Celestina seems to blame lovers for the injury their desire causes, but she certainly takes no responsibility upon herself for getting involved, manipulating both Calisto and Melibea, corrupting Calisto's servants, and the like. All of the harm caused by the relationship between Calisto and Melibea has to do with Celestina's own involvement and her influence on Sempronio and Parmeno and on Elicia and Areusa (women who work in her brothel).

To Celestina, Sempronio later says,

Don't you know that men esteem most those things which they find most difficult to achieve?

He wants to convince her to extort more money from the unsuspecting Calisto by keeping him separate from Melibea a while longer. This statement seems to be largely true in the play. Sempronio can get women easily from Celestina, so he doesn't value them. He, however, cannot get money easily, and he seems to value it the most. The statement seems to be pretty true of humanity in general. We often want what we can't have, and then once we get it—if we get it—it sometimes doesn't seem quite as grand as we imagined it would be.

After Calisto's death, Melibea aptly states,

We never know our happiness until we have lost it!

Again, this seems incredibly true in general. There's a reason we have the saying: You don't know what you got until it's gone. We often take for granted the things and people that are in our lives, or we don't really recognize their true value to us, until something happens to them. It seems to be a sad fact of life that people don't realize how happy something or someone has made them until that person or thing is gone.