The story I heard about Edison was that he invented a machine to tally the Senate's votes. They were not interested in it. So he had an invention without a market.

Before he invented the light bulb, he sat down and did a little basic arithmatic. Something like how many households are there in New York and how much does each spend on oil to light their household.

He had many inventions, I guess after a few debacles like the one with the Senate he relized that an invention really wasn't worth much unless it has some market value.