The Rare Ingredient Solution
When incorporating magic, potions, or powerful technology into worlds, these fantastic items and abilities will likely have a far-ranging and drastic impact on how the society and culture of a world functions. If a wizard can transmute any metal to gold, the economy crumbles (or at least shifts). If a healer can bring a person back from the dead then murder, duels, and war may be far more likely outcomes to any disagreement. If genies and wish spells exist, reality itself may be rewritten each hour and it would simply be impossible to get any work done. Worldbuilders will often overcome this problem (if they acknowledge it) by limiting the magic or technology that causes these outcomes. This limitation may come in the form of some rare or hard to obtain ingredient that is necessary for the magic or technology to function. In this way the world can avoid some of those drastic impacts because the magic or technology that would cause them is unusual and uncommon.
Having only a small percentage of the population demonstrating magical or fantastic ability is another version of the rare ingredient solution. In this case, the fantastic power itself is what is rare.
