Question

What made John D. Rockefeller such a successful businessman

Answer 1

He built his first oil refinery near Cleveland and after that it was kinda just like him investing until he became a business monopoly. 

Answer 2

The correct answer to this open question is the following.

What made John D. Rockefeller such a successful businessman was its tenacity, unwilling commitment to work, and his visionary mind.

John D. Rockefeller (1839-1937) started to work hard since age 14, in small tasks in Cleveland, Ohio. He worked really hard and seized some opportunities that by 1860, made him enter the oil business. He opened his first refinery in 1863, and by 1870, his Oil Standard  Company started to grow. Things did well and he started to acquire all his competitors until the Standard Oil Company became a monopoly.