Hakaras hatov is not only a beautiful middah, it is a middah which is dictated by common sense. This being the case, why do people have such difficulty showing their appreciation to those who have helped them? Moreover, it is clear from this week's Parsha that a lack of gratitude has been ingrained in mankind since the time of creation.
In the midst of the construction of the tower of Bavel the Torah tells us, "And Hashem descended to see the city and the tower that were built by the offspring of man" (Bereishis 11, 5). Rashi, citing Chazal, asks why it is necessary for the Torah to inform us that the tower was built by the offspring of man. Would we have thought that it was built by the offspring of donkeys or camels? Rashi explains that "man" (adam) mentioned in the above pasuk refers not to human beings but to Adam Harishon. The Torah is emphasizing that their behavior resembled the behavior of their forefather. Adam, after eating from the eitz hadas, blamed his wife and thereby displayed a lack of gratitude to Hashem for giving him a wife. So too, the builders of the tower whose intention was to fight with Hashem, were ungrateful to He Who saved them from the flood. Although Adam's lack of hakaras hatov was displayed toward Hashem and not another human, it is clear that he too had difficulty with this middah.
Rav Wolbe writes (Alei Shur vol. II pg. 280) that there are two basic reasons why people do not show hakaras hatov. The first reason is that people simply think that they deserve everything they receive so there is no reason to thank the benefactor. A child is born without intelligence and by the time he is old enough to comprehend what is going on, he is already used to being healthy, well fed, dressed and taken care of. Additionally, a person is born with a sense of egocentricity that places him in the center of the universe and causes him to act as if everyone around him has been placed there simply to serve him!
It takes a lot of work to free oneself of these feelings and to come to a realization that absolutely nothing, including life itself, can be taken for granted. One who comes to such a realization lives in a bright and happy world for he perceives everyone around him as active members of a huge world of kindness. In contrast, others look upon the doctor, bus driver or storeowner as people who do their job for no reason other than to make money, and therefore, he finds no reason to thank them for their services.
The second reason that prevents people from expressing gratitude is the feeling of indebtedness to their benefactor. Acknowledging that you benefited from another person means that you owe him something in return, and no one likes to feel indebted. Hand a child a candy and he'll snatch it and run away without saying thank you. (Rav Yeruchom Levovitz would say that if you want to do a complete favor for another person, immediately after doing the favor you should ask the beneficiary to do a small favor for you thereby preventing the feelings of indebtedness).
Hakaras hatov might be a difficult middah to master, but it is well worth the investment. It is the key to good interpersonal relationships, a great marriage, and a real connection with our Creator!