[marketer]

Another one is not being good at marketing.

Marketing can be a huge grind. Being able to build buzz about your product, or get mentioned in the press, or find customers is very time-consuming and requires a lot of creativity.

[nickpinkston]

You know you've got a shitty co-founder if they can't build a product or sell one. Real hustlers make it happen - "idea guys" need not apply.

[bane]

I agree, there's nothing that can drain the life out of a company with limited resources than the infinite time suck of an idea fairy on the loose.