During Roberts Rebellion, while the would-be King was out on the battlefield, Stannis was ordered by his elder brother to remain at Storms End and hold the seat for the family. This he had to do for a year, while the castle was besieged by troops led by Mace Tyrell. To survive, Stannis and his small army - only around 500, against tens of thousands of Tyrell bannermen - had to eat horses, cats, dogs, and eventually even rats as the assaults came from land and sea, meaning there was no way to get supplies. That was until Davos Seaworth managed to smuggle in onions, which helped them survive long enough for Ned Stark and his men to arrive and end the siege. Had Storms End fallen then many would have lost faith in Roberts cause, and abandoned him completely, while the Tyrell army wouldve been able to join in with the rest of the war, making it a much more difficult fight. Despite the importance, its an overlooked part of the Rebellion, and Stannis didnt even get made Lord of Storms End for his trouble. That honour went to his younger brother Renly, while he had to make do with being named Lord of Dragonstone instead. Despite the snub, he remained loyal to his new king.