This follows the sad story of the siblings Darkfur and Brooktail. Brooktail died on a patrol that Darkfur was on, and he beat himself up for losing his little sister like that. Then his brother, Redleaf, visited him, and told him that he had to snap out of it, pull himself together, and stop neglecting his duties. He said: "It is still alright to mourn her, but the clan should not suffer because one of their best warriors neglects his duties." Then, more gently, he added: "And plus, you'll see her again in Starclan."
@JupiterWolf & Erin Hunter