|Image via Der Wik|
The reason that you use your thumbs when you play the play the piano is thanks to C. P. E. Bach, son of Johann Sebastian Bach. Bach fils was famous at an early age due to the combination on his famous father, but in no little part to his own quite impressive musical talent. He not only performed and composed (notably for Frederick the Great), but was a teacher.
As part of this he wrote Versuch über die wahre Art das Clavier zu spielen An Essay on the True Art of Playing Keyboard Instruments) which more or less instantly became the definitive treatise on how to play keyboards. Mozart, Haydn, and Beethoven all regarded it as invaluable.
And it changed the way people played piano - remember, you use your thumbs, right? That was in his book.
It also changed the way that people composed for piano, leading to what we more or less recognize as modern piano. The son of the greatest classical composer opened the door to the modern.
C. P. E. Bach was born on this day in 1714.