Keep your word.
Early in David Rossi's career, he had a case involving the murder of parents of three young children. The children's grandmother gave Rossi a charm bracelet with the children’s names inscribed on it to always remind him of the case.
Twenty years later, the BAU helped Rossi finally close the case. Though the three now-adult children had long since lost faith in Rossi solving their case, he kept his promise and brought them closure.
"Damaged" (Episode 13, Season 3 of Criminal Minds)