Game of Thrones Season 1 opens in the North, territory ruled by the Starks since time immemorial. Their seat of power is Winterfell, where the family has lived since their ancestor Bran the Builder, first laid the foundations back in the waning days of the Age of Heroes. The saying, "There must always be a Stark in Winterfell," is proof of the area's entrenchment in the old ways. However, this Winterfell Game Of Thrones theory suggests there may be more to it than that.
Brandon Stark, known as Bran the Builder, was the founder of House Stark, with myths suggesting he was initially related to Garth Greenhand, founder of House Gardener in the Reach. While it's not clear if Bran did everything attributed to him by legend, it is generally agreed he was the first "King of Winter." He originally built the Wall and the Night's Watch castles that divide Westeros from the Far Snows, as well as Winterfell for his family to live. (Hence his "Builder" nickname.)
It is not clear if Bran also came up with "Winter is coming," or "There must always be a Stark in Winterfell," but as Season 8 arrives, fans are starting to suspect they do.
The Wall was created to keep the Night King out, to protect humanity from another attack. Bran didn't just build it from bricks and ice. There's magic embedded in it, preventing a partial wight like Benjen from getting too close. This magic kept the Night King on the far side until he had a dragon to counter it.
Bran worked with the Children of the Forest to make it that way. Why wouldn't he do the same for his own home?
"There must always be a Stark in Winterfell" was a phrase fans heard a lot in Season 5, viewed by Sansa as proof no one could hurt her in her own home. That was quickly disproven. What if, instead, the phrase refers to the magic the Children baked into Winterfell as a security system, which only works as long as Bran's family dwells there?
The Stark phrase "Winter is coming" was always understood to be a warning. Fans no longer see it as the inevitable changing of the seasons, but a reminder of the Night King's possible return, and the winter-like blizzard that heralds his arrival. Likewise, the name of the Stark home, Winterfell, is now suspected of being the spot where the Night King was defeated the first time, where winter fell. The necessity for a Stark to be in Winterfell makes sense as part and parcel with them.
It also seems like the sort of deal the Children would make. It forcefully assures a family allied with the Children would rule the area, in exchange for protectionist magic. Sadly, man's short lifespan and memory would render it moot in only a few generations, leaving behind just a phrase.
Will Winterfell stand as long as a Stark remains inside? Will the Night King's trap in the Battle of Winterfell be to draw all four out, leaving Winterfell to fall? Fans will find out when Game of Thrones returns April 14.