Reminds me of the bit in Jekyll and Hyde where it turns out the doctor's alchemical formula only worked in the first place not because of the salt he using, but because of a unknown trace contaminant in the salt.
Also, of course: "instead of bobcat, package contained chair".
> it turns out the doctor's alchemical formula only worked in the first place not because of the salt he using, but because of a unknown trace contaminant in the salt
"In March 2007, engineers devised a manufacturing process for Fogbank. Unfortunately, the material turned out to have problems when tested, and in September 2007 the Fogbank project was upgraded to "Code Blue" status by the NNSA, making it a major priority [...]
The experience of reverse engineering Fogbank produced some improvements in scientific knowledge of the process. The new production scientists noticed that certain problems in production resembled those noted by the original team. These problems were traced to a particular impurity in the final product that was required to meet quality standards. A root cause investigation showed that input materials were subject to cleaning processes that had not existed during the original production run. This cleaning removed a substance that generated the required impurity. With the implicit role of this substance finally understood, the production scientists can control output quality better than during the original run."
Also, of course: "instead of bobcat, package contained chair".