Perhaps one trait I have learned well from my parents is how to say "No" to requests of time and money. When it comes to friends and family, there is a temptation to say "Yes" to every request because it feels good to help the people you value. But often times it comes at the expense of your own personal goals. There is definitely a time and place to say "Yes". But the difficult part is figuring out when to say "No" and do so gracefully. "Yes" to that new car, "Yes" to helping out at the bake sale, "Yes" to picking up your friend from the airport. All of these things can be great values. But what if the new car comes at the expense of your children's college? What if the helping at the bake sale means skipping a date with the woman of your dreams? What if picking up your friend from the airport means losing your job because it was the 5th time this month you left work early?
It takes self-discipline to avoid the immediate gratification in order to achieve your long-term goals. It does not mean you can't help others, and in fact, figuring out how to say "No" gracefully can be beneficial to both you and the other person. Instead of buying a car, you and your kids can learn how to fix the car you have. Instead of helping at the bake sale, maybe you could recommend 3 other people who might be interested. Instead of picking your friend up from the airport, maybe you could recommend a shuttle or taxi service - something your friend may not have been aware existed.
In academia, I have seen how the failure to say "No" has affected students' and academics' ability to do their job well. Some academics fail to say "No" to their co-workers and end up working on 20 different committees. Students fail to say "No" to their family or friends and neglect their homework until the last minute and have to spend an all nighter in order to finish.