The problem answering this is that the hardest part of starting a business is dependent on who you ask.
I, for instance, have no real stumbling blocks with finance.
I mean, I have three degrees in economics and my wife is a commercial banker – we got this.
You, on the other
If you are serious about entrepreneurship, the answer seems to be to get a cofounder who complements you.
Everyfounder (or set of founders) has a different take on the hardest parts of building a company. And those same founders will have different takes on the easy parts. Talk to two talented software engineers who founded a company and you may find that recruiting, managing, or marketing are perceived as the most difficult issues. Talk to the marketer and people manager who founded a company down the street, and you may hear just the opposite.
-Rand Fishkin, Lost And Founder