Promises Promises

A friend of mine recently returned from a trip to America. She told me that most airlines had instituted a new policy of limiting a passenger to one suitcase. An extra charge of 50$ would be imposed on a passenger who wished to travel with two suitcases.
The woman told me that someone had asked her and her husband to buy a number of sefarim for him. When she apprised the man of the new airline policy, he said that he would contribute to the cost of the extra suitcase.
When she returned from her trip, my friend brought the sefarim to the man's house. He asked her for a receipt of the books and paid her in full. However, he had forgotten that he had promised to contribute to the cost of the suitcase and my friend was too embarrassed to remind him.
We've got to be careful with our words and promises. The following story relates how a tzaddik remembered to fulfill his words, many years after he had uttered them.

When Rav Yaakov Kamenetzky, who was renowned for his devotion to the truth, turned 80, he began donning an additional pair of tefillin, known as the tefillin of Rabbeinu Tam, each morning. Because there is a legal dispute regarding certain details about the writing of the parchments in tefillin, some virtuous individuals have the custom of wearing a second pair to fulfill the opinion of Rabbeinu Tam. Although Rav Yaakov certainly possessed the piety required for one who wished to take on this stringency, some of his students were puzzled by the fact that he had never done so previously. What suddenly transpired which made him change his practice?
When they asked him about this, Rav Yaakov explained that many years previously, an elderly Jew in his minyan began to put on the tefillin of Rabbeinu Tam at the end of the morning services. One of Rav Yaakov’s students asked him why he hadn’t also adopted this praiseworthy practice. In his humility, Rav Yaakov attempted to avoid the question by noting that the other man was much older, adding that if Hashem would allow him to reach that age, perhaps he would also adopt the practice.
Although the comment was said only casually, Rav Yaakov immediately worried that his commitment to truth obligated him to fulfill his words. Upon ascertaining the age of the man, Rav Yaakov waited many years until he reached that age, at which point he immediately adopted the practice in order to keep his “promise.”
http://www.shemayisrael.com/parsha/alport/archives/matos69.htm