Perhaps it’s not a coincidence that Jupiter being in someone’s 1st house or having Jupiter rule their rising is sometimes described to be a placement that can “bring luck wherever the individual goes”.
Let’s look at Sagittarius and Pisces (Jupiterian beings) separately to evaluate this.
Sagittarius is often pinpointed as an optimist. The Law of Attraction states that you attract what you think. Therefore, an optimistic Sagittarius will only attract good things to their life, appearing “lucky” to the outside world. In addition, many great philosophers (Philosophy is a Jupiterian subject) followed this law and believed in it.
Pisces, on the other hand, attracts fortune through fantasy. A Sagittarius will simply expect or hope for the best while a Pisces will fantasize about what they wish would happen/be happening. This channel of thought enforces the Law of Attraction and gives a Piscean what they desire. This ease of manifestation is also why Pisces may easily bring their own self-undoing. Pisceans are known to soak up emotions that are around them. Once this gets into their head and messes up their thoughts, then undesirable events happen; this chain of events falls within the Law of Attraction.
Of course, at the end of the day, Pisceans are still under the care of Neptune: a guide who will release Pisces to the clouds without a tie to bring them back to reality. This could be the difference in how Pisces and Sagittarius experience luck. Sagittarius is very grounded and eager to learn as well as initiate action while Pisces is busy dancing in the clouds.