I have found that the two biggest causes of having to fire an employee at an early stage startup are a lack of culture fit, and the inability to Get Shit Done. I don’t care how smart someone is - if they are unable to work hard and crank out a large amount of high quality work, they will weigh down your startup.
I’d say this applies not just to start-ups, but to any company looking to be at its most productive and efficient. Hire for GSD.