When you think of the creative leaps required to get to so many new technologies or processes, you come to realize that most of the time the benefits were not the intended results. There are so many variables that lead to things we take for granted, it is simply the by-product of intelligent, educated people working on creating and combining to get a result. That can, on occasion, lead to an unintended discovery that is quite useful.
Since science is about testing theories or perceptions, it makes sense that many discoveries are accidents that had huge impacts on medicine and the economy. A small sampling of these happy accidents include penicillin, the microwave, velcro, teflon and vulcanized rubber. Coca-Cola was also an accident, and although it's bad for our health, I guess it's good for dentists.
Yes, most scientific discoveries are accidental. If they weren't accidental, they would not likely be discoveries. If a scientist knew what they were looking for and where to find it, there would be no discovery involved. It's wonderful to see all the new discoveries that come up in "accidental" ways.
Most discoveries start when scientists make an attempt to fix a problem with their experiment. In an attempt to explain these kinks, scientist may come up with a new discovery. These are not happy accidents, but clever exploration of unexpected results. A good word to describe this scenario is serendipity.