You should not let down people that depend on you.
Jim promised his brother to come pick him up from soccer practice in his car.
Jim wants to drive to a girl's house.
Jim takes his brother home from soccer practice quickly before driving to the girl's house.
Jim forgets about his brother and goes to the girl's house.
Jim's brother is glad that he can rely on Jim to keep his promises.
Jim's brother has to walk home from soccer practice which takes two hours.