Luck and Intelligence
It's directly related to potentials that exist within the family line, and within one's own self, warded respectively by the hamingja or kyn-fylgia, and the fylgia. The disir are the clearing-house for the sculd of the family, which consist in both debts and potential powers. Potential is itself a kind of debt which must be paid off through investment and development in order to come to fruition. Failure to develop potential inhibits flows of luck just as much as committing violations of others' rights, which throw debt into the pool.
The disir give you the matching funds for your demonstrations of intelligence and initiative. As you earn, you receive. But earning involves passing the learning-curve, not banging your head against the wall until it bleeds and calling that effort. Inertia is the way of giants ; intelligence is the way of the Gods.
Once you get that, you'll get the essence of what belongs in Midgard and what doesn't, what allows it to be Midgard, and what transforms it into Jotunheim. Even customs can become giantish when they stand in the way of intelligence. And no, intelligence is not something that comes from a distant and far-away elite, ivory tower, but listening to the intelligence from within, which is sometimes nothing but the disir whispering into our ears as they dialogue with the local landvaettir.
Stupidity, inertia, brute force, custom that steps outside of sustainable and enlightened pragmatism : these are not the ways of the Gods, but the ways of Giants. We are awarded by our disir according to our evolutionary advances.
The ways of Fire and Ice may seem stronger. The glaciers seem to have more holding-power due to their incessant inertia. The flames seem to have more quickening due to their rapid leaps. But it is in the Middle where a sustainable world is created. Fire is too quick, too instantaneous, burning and consuming in its path. It quickens, but will not hold. Ice is too slow, too unmoving, hedging in and freezing growth. It is in Mimir's Well, there in the middle, where the Good grows, slowly, slowly, layer upon layer, not too fast and not too slow. Goldilocks and the Three Bears holds the secret to the entire Teutonic philosophy.