Our greatest weakness lies in giving up. The most certain way to succeed is always to try just one more time.
One might think that the money value of an invention constitutes its reward to the man who loves his work. But... I continue to find my greatest pleasure, and so my reward, in the work that precedes what the world calls success.
Anything that won't sell, I don't want to invent. Its sale is proof of utility, and utility is success.