The island of Madeira was often a last port of call from the 15th Century for sailing ships head to the New World or the East Indies. The local wine loaded on to the ships would quite often spoil because of the heat and motion of the voyage. To prevent this from happening, a small amount of alcohol distilled from cane sugar was added to bring up the strength and kill unwanted bacteria.
The heat of the voyage, especially in the confined holds of the ships, plus the motion of the ship, transformed the wine, giving it the familiar tart edge that distinguishes it from port. One shipment was returned after the long round trip, and was found to be popular with customers, who preferred the new taste, so producers began sending the wine on the round trip to age it. It was known as vinho da roda, wine of the round trip, and initially could not be produced any other way. Thomas Jefferson was an early fan, and the Founding Fathers toasted the signing of the Declaration of Independence with it.
The long sea voyage was expensive, so the producers experimented with ways to reproduce the conditions of the voyage. At first they stored it in rooms exposed to the heat of the sun, then developed the modern method of heating the wine in steel vats heated by running hot water. This, they found, replicated the conditions of a tropical voyage and produced the widely admired wine we know as Madeira.
The development of the wine illustrates one way in which progress is sometimes made. It starts with an accidental discovery, but it also requires opportunism, to spot the result and to seize upon it. It then takes initiative and application to develop the discovery and turn it into a technique. The discovery and development of penicillin after the famous discovery of mould in the petri dish affords another example. Some discoveries might start with an accident, but it takes people smart enough to spot it and resourceful enough to use it.