Cancer plans a Sunday months in advance, down to who brings the wine and which blanket goes on which chair. Sagittarius wakes up Sunday morning and wants to drive to the coast because someone mentioned a beach two hours away. This is the friction that will not go away on its own, because Cancer is cardinal and Sagittarius is mutable, and those two move through the world on completely different clocks. Cardinal signs like Cancer initiate, they like to set the plan in motion and see it through. Mutable signs like Sagittarius adapt, they would rather leave the plan loose so life can rearrange it. Left alone, Cancer starts to feel like the only one steering, and Sagittarius starts to feel boxed in before anything has even gone wrong.
The good news is that this pairing can actually balance rather than clash, if they let it. Cancer gives Sagittarius a reason to come home to the same address, a fridge that gets restocked, someone who remembers how they take their coffee. Sagittarius gives Cancer permission to leave the house without an itinerary, to say yes to the beach even though the blanket situation is now unresolved. Jupiter's expansiveness meets the Moon's need for shelter, and when it works, home stops feeling small and travel stops feeling like abandonment.
The honest challenge is emotional pacing. Cancer wants to process a hard conversation slowly, in stages, with reassurance along the way. Sagittarius wants to say the blunt true thing and move on, sometimes before Cancer has finished flinching. Neither is wrong. They just need to agree, out loud, that speed is not the same as care.