The “Walk a Mile…” quest is an overarching story quest. When you get the quest “Walk a Mile…”, you will also receive a call from Maria, as well as another quest named “Sole Mate…lla”. After completing “Sole Mate…lla,” you will receive the quest “Portrait of Solitude.” After completing that quest, you will get the quest “Front of the Line”. Once you complete “Front of the Line,” you will be able to finally complete “Walk a Mile…”.