How to win Fortune

Do not hesitate to engage in any legitimate business, for there is no business in America, I do not care what, which will not yield a fair profit if it receive the unremitting, exclusive attention, and all the capital of capable, industrious men. 
Every business will have its seasons of depression — years during which manufacturers and merchants are severely tried — but every legitimate business producing or dealing in an article which man requires is bound in time to be fairly profitable, if properly conducted. 
And here is the prime condition of success, the great secret: concentrate your energy, thought and capital upon the business in which you are engaged. Having begun in one line, resolve to fight it out on that line, to lead in it; to adopt every improvement; to have the best machinery, and know the most about it.  — Carnegie.