Confucius said: “When the father is alive, observe his son’s intentions. When the father is dead, watch his son’s conduct. If after three years he has not deviated from his father’s path, then he may be called a dutiful son.”
Confucius saw no room for compromise in following the obligations of filial piety.
Three years was the standard period of mourning. The very fact that he feels compelled to mention it suggests that this convention wasn’t followed as strictly as he thought it should be.