Serendipitously Discovered Serendipity

One of the highest wattles the English have built is the rich vocabulary of their language (English approx. 500'000 words, German 185'000). This makes it exceptionally hard to master the English language (besides of my lousy spelling abilities). On account of the affluent word-hoard, the English language is also a source of fortunate discoveries by accident. My serendipitous discovery of today is Serendipity.

The English are indebted to the author Horace Walpole for the word serendipity:

". . . this discovery indeed is almost of that kind which I call serendipity, a very expressive word, which as I have nothing better to tell you, I shall endeavor to explain to you: you will understand it better by the derivation than by the definition. I once read a silly fairy tale, called The Three Princes of Serendip: as their highnesses traveled, they were always making discoveries, by accidents and sagacity, of things which they were not in quest of: for instance, one of them discovered that a mule blind of the right eye had travel led the same road lately, because the grass was eaten only on the left side, where it was worse than on the right--now do you understand serendipity?"

Some serendipitous discoveries and inventions:

• Alexander Fleming's discovery of penicillin
• The discovery of the cosmic microwave background radiation
• Alfred Nobel's discovery of blasting gelatin
• The discovery of polyethylene
• The invention of Silly Putty
• The invention of Post-it notes
• The discovery of the psychedelic effects of LSD by Dr. Albert Hofmann
• Archimedes' Principle.

Do you know more examples of serendipitous discoveries?