(p. 265) In his business and research projects, Edison became more timid as he became older. While in his thirties, he had had the energy to tackle a problem that had seemed to many to be insoluble: the “subdivision” of the electric light that would make indoor use technically and economically feasible. In his forties, he had continued to dream big and put his winnings from the electric light business into the mining business. It had ended disappointingly, but he cannot be criticized for timidity. In his fifties, he did make another sizable bet. However, for this venture, pursuing the improvement of the battery for an electric car, he had financing from Ford that insulated him from personal risk. He continued to steer clear of risk in his sixties and seventies.
Stross, Randall E. The Wizard of Menlo Park: How Thomas Alva Edison Invented the Modern World. New York: Crown Publishers, 2007.