Asafoetida is measured in pinches while other spices are measured in spoons. The reason is that it is a concentrated resin whose raw aroma is aggressive and whose useful flavour only appears after it meets hot fat.
It is a resin, not a ground seed or bark
The material is dried sap tapped from the root of a plant in the same family as fennel and cumin, then hardened into lumps.
Because it is a concentrated exudate rather than a whole plant part, the aromatic compounds in it are present at far higher levels than in any powdered spice.
What is sold as powder is almost always the resin cut heavily with flour or gum, which is why quantities differ so much between products.
Sulphur compounds do the work
The powerful raw smell comes from sulphur-containing compounds closely related to those found in onions and garlic.
Those compounds are volatile and unstable, and heating them in oil breaks them down into gentler derivatives with a rounded savoury character.
The transformation is why the spice smells unpleasant in the jar and tastes like allium in the finished dish, and why adding it to a cold or finished dish fails.
Fat is the required medium
The active compounds are soluble in fat rather than water, so they disperse through oil and then through the whole dish.
Dropped into a watery pot, the resin clumps, disperses poorly and leaves both raw patches and unseasoned ones.
This is why it goes into the tempering at the beginning, in hot oil, usually immediately after the seeds and before anything with water in it.
The quantity is unforgiving in one direction
Too little is invisible in the finished dish, which is a mild disappointment and easily corrected next time.
Too much dominates everything and cannot be balanced out by any other ingredient, since nothing else in the pot occupies the same register.
The asymmetry is why every traditional instruction errs low, and why cooks judge by the smell of the oil rather than by the measure.
It fills a specific gap in the repertoire
Communities that avoid onion and garlic still need the savoury base those ingredients provide, and asafoetida supplies a close approximation from a plant that is not an allium.
It also has a long-standing role in legume cooking, where it is used alongside the pulses in a great many regional preparations.
That combination of substitution and tradition explains why a spice this difficult to handle remained a pantry staple rather than a specialist item.