Hard labor has been the norm in our society since before it was a society. For thousands of years, people who worked harder got more done and were less likely to, y'know, starve.
see http://www.zpub.com/notes/idle.html it is a good read
You literally worked for the MAN, a servant, and lived much more in a collective as we could stomach today. Individually going out and "making it"? Not realistic.
Things were slow. Harvest would happen in a few months, your market was local and expanding a business unrealistic in many cases. Travel was super slow and dangerous. Society was restricted in many ways. Wars, fires, famines could happen anytime and destroy everything you had.
Work was usually physically hard, and food might be scarce, and you better not get ill or injured, right? Are you sure putting in 150% would be wise under these circumstances?
But I'm curious if you've some other aspects I am missing, particularly anything authentic from literature describing the ambitious, hard working people you have in mind.