http://revach.net/article.php?id=4271

Section:  Avodah   Category: Ahavas Yisroel
Rav Chaim Zaitchek: The Paradox & Pain Of A Thank You
My Rebbi once said that if someone greets you with a sour face in the morning, don't be so egotistical to think that you are the only one in world on his mind.  He bad mood probably has nothing to do with you so there is no need to take offense. 

What really boggles the mind of Rav Chaim Zaitchek though, is how could it be that although Hakora HaTov is such and important Middah, people avoid it like the plague.  They stay as far away from their benfactor as possible.  They avoid his presence at all costs.  Shouldn't they run after the person who has helped them and try to be grateful?

He explains that by definition we owe a debt of gratitude to someone who helped us when we needed something.  We were in a bad spot and couldn't get out until this person came along.  While there is great appreciation for the person who helped us, this appreciation comes with a vivid flashback to our predicament.  People do not want to remember the bad times and that is precisely what our benefactor's presence forces upon us.

With this he explains how Paroh and Mitzrayim who owed their entire existence to Yosef and Bnei Yisroel could not only conveniently forget Yosef, "V'Lo Yada Es Yosef", but our mere presence and the bad memories it invoked because a thorn in their size.  Instead of appreciating us, our sight was repulsive to them until they eventually took all their fury out on us.

So next time someone who you did a tremendous favor for keeps a cool distance from you, don't be furious be understanding.  Give him his space and know that the further he stays from you, the bigger favor you must have done for him.  Most of all, if you want him to be your friend, forget the incident and don't keep reminding him about it.